PlayStation 3 software is not region-coded, well it is but it isnt LOCKED to a specific region. The hardware itself has regions.
Yes you will be able to play US/JP/PAL games of PlayStation 3 software. You will NOT be able to play other region of PS2 software, that is still region locked. So if you get a US PS3 you will not be able to play PAL PS2-games.
Remember that Blu-Ray movies are also locked, not all of them but some are. Warner titles are region free, most Sony Pictures titles are free, Disney/Buena Vista are region free as long as it isnt NEW movies. FOX movies are almost always LOCKED.
DVD movie playback is also still region-locked.
Yes the stores are different. US store is where all the action is, but fear not its easy to register a US account so you will be able to download all the stuff our american enemies get. My Swedish VISA even works on the US-store so I have bought a few games over there.
I recommend setting up an account for each region, Europe/Australia (same content I think, though the Australian store has some music videos which we havent got on our EU-store yet), America and a Japanese-account. This way you will be able to access demos from all over the world.