I always have been a little iffy about the 10 year life cycle. 5 years maybe, but not 10. Also Sony never said they would wait 10 years to make a new console they just said the ps3 life cycle would last 10 years. Development costs to make games are getting pretty high.
Making a system twice as powerful should make games more expensive to make. So if they released a PS4 that could play PS3 games(and if both have the same processors I don't see why not) then dev can choose whether they want to make games to PS3 specs or if they want more power they can use the PS4.
I have a feeling I could I worded this post a little better but I think you know what I mean lol.