Hmm.. how could a PS4 work for 6-7 years and a PC only for 3-4 years, when they re using the same architechture. Also if the PS4 life cycle goes beyond 6 years, it means games are being developed for them in large numbers. Since the architecture is same, these will be ported to PC making the life span of a PC 6 years too.
And please dont compare it to PS3, PS3 was using Cell arch. So porting PS3 games to PC was difficult. This is no more the case, so all games except the exclusives (may be), will be ported to PC... ie more games to play and more life span for a PC.
Also when you are comparing the cost of the PC and PS4, why dont you add the cost of buying the PS4 games (for 6-7 years).
And pls open the steam site and check the games available for PC, before commenting that PS or xbox have more titles...
P.S: One more thing emulating PS4 games on PC would be easy due to the same x86 arch.; so you would be able to play all ps4 games on a pc. Same may not be possible other way around...