They don't cost same. A500 especially is much cheaper. And these are MSRP prices. In three or four months, the prices will drop. When
A700 was launched, it's MSRP was $1,400. A500 is like $749? That's about half.
Well, the price will drop, undoubtedly (although I doubt it will drop that radically in 4 months, and the A700 will also drop in price as well). So if you are buying it when the price drops, fair enough. And, for the record, I view the A500 & A550 as two very distinct cameras appealing to very different people (which is why I posted it here, as opposed to in the A500 thread).
Also, not because they are about the same price now, doesn't mean that one is a better value than the other. The feature sets are very similar and they cost around the same. Why limit your options otherwise?