Because Sony messed up.

This may be true, but I don't think the question was "Why can't the PS3 run PS2 games in 1920x1280 with 16xAA and 16xAF?"  If the PS3 can render PS3 games at 1080p, it should be able to render (not upscale) PS2 games in 1080p.  And if you've only got a 720p display, it can probably throw in a little AA and AF while it's at it.

Because PCSX2 has been in development since about a year after the PS2 launched. Also, rec specs: 4 - 5 Ghz machine 1024MB RAM X1800 / Geforce 7800 GT And thats to be running the games at (an average of) 30 fps. I've been following the development for PCSX2 since its inception.

Sure... but it was developed blindly, from scratch, by a bunch of basement programmers. Sony's programmers have every advantage by comparison. And where a PC has to do all of its emulation by brute force because it's such a fundamentally different machine, the PS3 should be much more compatible - I mean, as far as I know, most PS3's in the world still actually contain the PS2 in its entirety within the case.

I'm no tech expert, but I don't think I buy the technical limitation theories. So, I dunno... maybe it's in development but it's taking a really long time, or maybe they made a business decision not to bother with it. Which would be a huge shame, if you ask me. 

Borkachev - The machines with the PS2 inside do have ~100% compatability, it's the ones who don't have the hardware inside that need the software. Also, you have to remember that PCSX2 is an open source project with a huge following, meaning that a lot of fixes in the past were made by people not part of the team. And, it's obvious that Sony do have an advantage, considering all my games now work (excluding a monster hunter demo) since 1.8 (I tried all the ones that didn't work before hand). I'd say for every 1 year of PCSX2 progess = ~a month of Sonys progress, meaning that support will be around ~98% by the end of the year. (if they keep at the same rate, that is).

Sony sees it like this: You already own the PS2 game. How would they make additional money, if people already think the PS3 emulates well?

 You mean in any way other than improving European BC by huge amounts?  Or by introducing a smoothing filter in addition to upscaling?  Seems like each release they are improving the software emulation noticeably.  Or were you just trolling?