I can vividly remember the PS3 being launched, they're doing another one ?
5-7 years between systems is the usual life cycle of a console generation, and the PS3 came out in 2006! Sony promised it was going to be a 10 year system, but it actually IS about time to start developing a new one for release in 2 or 3 years… even if we don't really need the generational upgrade yet.
It just doesn't feel like it because its been that long because still hasn't been truly tapped yet. The high price point of the PS3 initally, and the huge installed base of the PS2 kept the PS2 dominant a lot longer into the life of the new system. PS2 still had great new games coming out up until maybe a year or two ago... and its still getting ports of some games now.
So a lot of people are still on the PS2 and only just now getting ready to make the hop to the PS3 and hi-def televisions and whatnot, and blue ray still isn't really the dominant format compared to dvd and stuff. Plus, a "next gen" hardware jump might be able to produce better graphics (so that it looks like fmv all the time) , but it'll never be as huge a graphic visual leap again as it has been in the past, since we're already getting photoreal movie quality super elaborate visuals that take developers years to create.
It'll never be Nintendo-Super Nintendo or Genesis-Saturn or PS-PS2 jumps in quality again. Even the switch from PS2-PS3, while allowing for more elaborate visuals and bigger enemies and stuff, still wasn't a huge leap from what the PS2 could do at its best.