The closest usage of the word classic in the context we utilize it means "having lasting significance or worth; enduring."
How can you detirmine that when two of the consoles are barely cold and used copies of their games, accessories, and hardware litter used game stores across the country, and the third is still a ongoing concern at present for many (Or has just recently been left behind by others) and appears as if it has some life left in it?
Like it or not, but that generation is still a ongoing concern for many gamers across the country, still is being widely sold used and new, and at least one of the platforms still has significant development occurring for it and millions of consoles sold just in 2009.
I think we utilize the term classic to signify more than just that production of consoles and games for it has ceased. It means the system has ceased to be a ongoing concern for the vast majority of former users for it, and is something people will start to look back on with fondness.
It isn't a term that describes a console that is still on store shelfs being sold new at every retailer that sells videogames.