Well... I guess, since most of the hardware development probably took place in Japan (beside Cell and RSX), and the Japanese are always at the forefront of all sorts of home appliances, they didn't "see" the problem in the US (as it wasn't present in Europe either, with the HD Ready label). I mean, there are things, you might not consider at all when working on stuff like this.
Before I bought the PS3, I was actually suspecting that all games always ran at native resolution, even on PS2 or PS1 (well, I was still young and at school at the time
).
But true, Sony knew that many of their own older TVs didn't support 720P (which, btw was one of the most moronic moves of the TV industry by far^^) and thus had problems with the PS3.
At first, the PS3 couldn't even playback BluRays at 720P and your tv had to support 1080i to view HD on your TV, as the PS3 couldn't convert down to 720P.
They should also let me set up, which resolution a game should default to. I mean, I have a 1080P tv, so naturally, I set up the PS3 to 720P and 1080P, but some games thus default to 1080P although their software scaling is very bad. I have a Bravia, which indeed has quite a good scaler in comparison to my mothers Samsung (older model though).