Off course there will be a PS4.
But what we see now is that Sony was taken by surpise:
Both competitors ( MS and Nintendo ) are doing well because of their advantages:
The Wii is at a low price-level and appealing to a different ( and bigger than expected) player-base, the XBox had a year advantage and an easier to program architecture.
Don't forget that the PS3 is a powerful machine, but Sony's biggest mistake was their price.
If it was $400 from the beginning, it would already be success at this moment, in spite of the larger xbox line-up of games.
I don't believe the PS2 had such powerful competitors, so this console war is not at all comparable with previous console wars.
But I think Sony learned a lot already from the PS3 and the competition, and when the PS4 will come in sight, they will have the benefit of an evolved Cell ( Cell 2 ? ) and BR technology ( 100 GB should be possible by then ).
If they are able to sell a more powerful console for the price of about $300/ E300 and an improved SDK to make it easier for 3rd party studios to design and develop games ( design for PS4 and compile for PS3 too) , it will be a lot harder for both Nintendo and MS to compete.
But that's all in the long distance future, let's see how the PS3 and others will do in the coming 52 weeks ;)
