Few reasons the PS2 keeps getting good sales:
Price. When you can get a system for $129 that still has decent graphics with the newer games, it becomes very attractive.
Games. God of War 2 and Guitar Hero 2 are very impressive, strong, great AAA titles that came out AFTER the PS2 was cancelled. Tell me a SINGLE system that has AAA titles once it's predicessor has come out. Nintendo moved Zelda: TP to Wii rather than GC-Only, MS moved everything (PDZ, PGR 3) to 360, ect, ect ect.
Library. The PS2 has, by far, the best overally library in gaming history (atleast to most people). At $129, it's easy to buy one and find a few dozen games @ $10 or $20 that are great.
The PS1 was similar. When you have an incredible library, price and support, a system WILL sell well regardless. Thats been the key to the winner of every console war. They've always had a good mix of innovation, dev support and good WOM. Atari 2600, NES, PS1 and PS2 were the winners due to those major reasons.
Back from the dead, I'm afraid.
