The concept of a system being "Designed for 10 years" is 100% marketing BS, you might as well repeat that "The best part of waking up is Folgers in your cup" ...
The reason the PS2 continues to sell is that it is dirt cheap, you can find inexpensive games everywhere (there is alwasy a bargin bin of PS2 games at most large retailers, there is a massive used section at most game stores and many garage sales have a wide assortment of games available); this (not technology) is why the market leading console always lives so long.
Sony's last shipments of the Playstation were between September 2004 and March 2005 so I expect the final shipments of the PS2 to be in about 2009 or 2010 ...
Stopping production of the PS2 would only annoy developers (do you think EA would like Sony stopping production of a system when they have dozens of pending projects?), consumers (do you think that single mothers will like that Sony wants them to spend $500 on a system for their 5 year old so they can play their spongebob games?), and retailers (do you think retailers want people comming in to buy God of War and the thing that makes it play only to be told that the $100 system was discontinued so that Sony could sell more of their $600 system?) ...
