I'm of the opinion that the PS3 could very well have a shortage. The Slim version hasn't been out for very long and sold a huge amount last year, most likely depleting most if not all of Sony's stockpile and you can't just suddenly conjure up more out of nothing.
People are making it out to be impossible, the Wii is seeing shortages after months of lower than expected sales followed by a flash in the pan so it's very likely that a refreshed system launching to record high sales (for the console itself) and for an extended period of time exceeded Sony's expectations considerably and thus said console is in short supply.
Overall sales seem good except for the PSP so PSP2 at E3 this year is pretty much confirmed at this point.