Hugo, I believe that changed prior to the last time they charged for an iPod software update.
The change in rules was approved on sep 23 2009 (see
http://www.reuters.com/article/idCNN2341502020090923?rpc=44 ); companies then have until 2011 to implement it. I believe Apple implemented it in the reporting of CQ4 2009 results (ie January 2010).
Don't think there have been any major updates since then.
And accounting rules inclusive, there have always been ways to get around that requirement. The bottom line is that those $10 updates brought in quite a few million dollars, so why not?
I think you're underestimating the cost of supporting multiple versions in the field (vs telling people to update to the latest free one), plus the general hassle and support questions about this.