I'll try and answer some of your questions as a Brit.

I was initially going to post and ask if this was somehow also being shown on British TV, but then I remembered that British TV seasons appear to be about six episodes long, unlike US seasons of around 22.

We use the term "series" rather than season. Most series aren't as short as six episodes, they tend to run for about half the length of a US season.

Oddly, the series that seem to be short are the comedy shows that have since been exported to the US (Coupling, Men Behaving Badly etc).

So US TV is split a bunch of different ways. Most of what you're likely to hear about over there is what we'd call broadcast or network TV. This is TV that's programmed by the major networks: ABC, CBS, NBC, Fox, and, to a lesser extent, WB and UPN. The idea is that these networks have local affiliates who are told what to show during ``Prime Time'', which is basically 8PM-11PM every night, plus some additional time on Sunday afternoon to evening, often for either sports or family programming. ( I believe that the networks also control a few hours around noon during the weekdays for soap operas, and maybe some game shows, but I don't know a lot about that.) The WB and UPN networks are fairly new, and they don't have as much programming, so they don't have shows for the entirety of Prime Time. Shows are sent to the local affiliates in advance via satellite where they are then rebroadcasted at the appropriate times. This was originally done over the airwaves, but Cable TV has been common in the US for twenty years or so. This is essentially a wide-area closed circuit system run over coaxial cabling run to each house that subscribes. Receiving programming over the airwaves is 100% free. Subscribing to cable is not.

During the time not reserved for the network programming, the local stations broadcast a variety of programming, from locally produced shows (including the local news), to syndicated series, to reruns of old shows. Often, they go off the air late at night (2AM or so), broadcasting nothing. Often they show infomercials during that time, instead, which are essentially 30-minute or hour long paid advertisements.

Ok, the UK works like this. We have (roughly) three different types of TV channel.

Firstly there is the BBC channels, until recently there were just two of these BBC1 and BBC2. They have no adverts, that really is zero adverts, not just not many adverts. BBC1 is the "mainstream" channel, BBC2 is the more high-brow specialist channel. The BBC channels are paid for by a TV licence fee that everyone who watches TV has to pay (about $170 a year per household).

Then we have the original non-BBC channels ITV, Channel 4 and Channel 5. These are paid for by adverts (but we have shorter ads on these channels that the eqivalent US channels), though until recently got some money from the licence fee.

Finally we have hundreds of other channels that are only carried on the new digital platforms.

BBC1, BBC2 and ITV all have the concept of regional opt outs. I think this operates in a similar way to the US networks in that there are only certain periods in the day when they get to show different shows. Where it is far simplier is that there is only a single timezone in the UK. I always struggle in the US to work out when shows are actually on...

We've got several different platforms in the UK:

- the original analogue terrestial broadcast TV network (which carries only BBC1, BBC2, ITV, Channel4 and Channel5)
- the Sky Digital satellite which carries hundreds of channels (including all the ones above)
- the Freeview digital terrestial broadcast network which carries a couple of dozen channels, aimed at people who only want a few extra channels but don't want to pay for them (designed to eventually replace the analogue terrestial broadcast network )
- the cable networks (there has been lots of take overs here, I think there are basically two cable networks left)

Most of the channels on the Sky platform don't commission their own shows, they just show stuff that other people have made. The BBC, ITV and Channel4 do commission lots of their own shows, though I think most of them are actually made by independant production companies now.

The terrestial analogue and digital networks are both free (remembering that everyone has to pay the TV licence fee). All the other networks are subscription driven (though there are some free channels on Sky, the BBC ones and lots of channels that just carry infomercials).

Many of the subscription channels on Sky also carry advertising. The adverts are shorter (and typically higher quality) than US adverts.

Programs are often cancelled with no warning and without allowing a show to begin to capture an audience. They have to be replaced. Sometimes they're replaced by reruns of another show in the primetime lineup, but they also schedule mid-season replacements, which are basically second-string programs that they didn't feel confident about starting a season with. There are generally not a full 22 episodes of these -- usually half that or less. They can get cancelled, too. If they like a program enough that was set as a mid-season replacement, they might do the original broadcasting of it in the summer. These are called summer replacements. They often take the spot of a program that was cancelled at the end of the regular season; the networks don't run summer reruns of cancelled shows, even if it went out on top.

UK shows are not cancelled mid-series, but I guess that is the benefit of a shorter run than US seasons.

So how does British TV differ? I know that most series only have about 6 episodes per season, and they say that there are no commercials, but I hear tell that that's not true (anymore?). Are there more series shown in order to fill up more time (like four times as many), or is there simply less original programming?

I think there is less original programming. The BBC channels probably have about 70% UK sourced programming. Some of the satellite channels are probably more like 80% US sourced content.

P.S. thankfully we tend to only get the better US shows on the main channels in the UK, I have been stunned by the crap that is on US TV that we don't get to see over here...