Why are you powering off to get out of the Netflix menu? You don't have to power off the PS3 to get back to the XMB.
There is only one PS3. The differences are all in bundling (games, controllers, internal hard drives). You can always install a bigger hard drive (this is officially supported by Sony) but depending on how you use the PS3 you may never need to. I don't use mine to serve media (I have a separate server) so the 40GB drive on my old PS3 has always been plenty.