Osamo was mainly pissed at the fact that American troops had been in and around Mecca ( I think) during the first gulf war, which is considered one of the holiest places for the Islamic faith. Though, had troops not been there, it would have been another place for Iraqi soliders to safely flee to. I'm not sure, but if Saudia Arabia DID allow permission, then politically, there would be no harm. Osamo is simply associates himself with one of the most extreme subdivisions of Islam, thus is justification is given.
Plus, I don't exactly remember hearing about other countries hating America much before 9/11, excluding countries know and blacklisted as supporting terrorism and admitting to using terrorism as a way to execute political feelings.
Also, justification for America not helping out other poor and developing countires is an outrageous claim or justification for something like 9/11. Many countries that could use the help are corrupt, and money pumped in could easily be used against intended reasons.
We didn't have the generalized and stereotypical "had it coming". Being a large, developed country isn't justification isn't a worthwhile reason. No country, its simply because of the fact America is also stereotyped as being the land of the free, or a promised sort of land for those wanting to start a new life. Really, its not going to be drastically different from some European country (exclude population/square mile/kilometer here).
I can't wait for someone to jump on my ass now, and point out a fact I didn't know or missed

Still though, its better to actually try and put some reasonable thought into something than jump on the bandwagon or base beliefs on a common or over propagated stereotype...