That is not how Sony worked for PS3, why did they put a blu-ray in the PS3 using that logic? No one had Blu-ray discs to play in a PS3, but Sony spent a fortune at a loss in order to provide this high tech facility. They get a return by controlling the HD retail film market media. They can do the same with next gen PS4 Blu-ray 4k ready. There is no way they would release a PS4 for a new lifecycle without 4k capability, even with no current userbase in existence.
But I expect by next year someone on gtplanet will own a 4k display and tell us about it. And then awhile after go on to tell us how good it is for GT6 on the PS4.
People might not have had Blu-Ray then but they certainly had HDTV sets, HD monitors and HD video content. The HD boom was taking off and Blu Ray was of course one side of the HD format war, as Toronado mentions.
4K on the other hand is nowhere close to being a mass market reality. We're nowhere near 4K broadcasts, we have no 4K footage widely available in other formats and therefore nobody has 4K displays and won't for many years to come.