The two megapixel difference is meaningless. As others have pointed out, the big issue is whether you want to buy into the Minolta "system" or whether you'd prefer one of the other systems. So far as I can tell, the big benefit of going Nikon or Canon is that you can rent exotic lenses if/when you need them. $100 for a weekend project is far cheaper than $5000 spent up front. There's no rental market for other systems.

The Olympus system, for what it's worth, seems attractive, both on price and on weight. $770 (at B&H photo) gets you an 8 megapixel E-Volt 300 with two lenses, the 14-45 and the 40-150mm zoom (double those numbers for 35mm equiv.). You're getting a "4/3 system" camera for which there will, theoretically, be a variety of third-party lenses at some point in the future. Today, at least, there are no image stabilized lenses, but you do get Olympus's clever anti-dust system.

The Minolta system gets you their IS sensor, which is a real feature, but I'd want to try it out in person to see if it really works for me. Also, the Minolta user interface seems much more complex than Nikon or Canon, so you'd have to spend some real time playing with it in a store. For what it's worth, B&H is pricing the 5D with 18-70 kit lens for $900. The "equivalent" D70 kit is $949.

If you go Nikon, Canon, or even Olympus, you get a fairly complete selection of wide-angle lenses. Minolta seems to be behind on this. If lenses like that matter to you, then you might want to look more carefully at the other vendors.