There's a lot of merit to that list of points, particularly the observation that many of the big PSP games are essentially scaled down versions of PS2 games (or PS3 games).
I'd like to say that there are definite key differences between Japanese and Northern American demographics with respect to preferences of portable vs. console gaming, but that still wouldn't explain the phenomenal success of the DS in NA.
Best I can tell, the DS is something just about any child who has an interest in games will own (I see a lot of kids with them in public places), in addition to being something an average adult can just pick up for Brain Age, or any number of the non-traditional adult oriented apps (cooking apps, exercise guides, crossword puzzles, sudoku, etc.). Plenty of games from Nintendo's core IPs for traditional gamers as well, in addition to big third party support.
The PSP on the other hand seems more like a media player device that has a decent library of core audience based games, which has lesser appeal to a broader audience. It's less of a children's toy, yet doesn't hold a terrible amount of appeal to the typical working adult who isn't an avid gamer and already owns an iPod.
Personally, it took me years before I finally bought one and it was ultimately to play the stack of PSP games I'd collected over the years that weren't available on any other system. If they had been, I'm going to have to say I probably would have skipped the PSP altogether, even as a core gamer.
