Imo it's a combination of several things, the first being that financially Sony can't really afford another hardware loss bruising again next gen, the amount of money they've lost not just because of gaming pretty much indicates a conservative approach. The U imo is partly a reason as Nintendo are smart enough to see their competitors are trying to recover from their losses so have opted to go full drive to force the issue with them, the U may not be a super computer but I'm certain it will easily be a good leap over this gen and more powerful then what some people initially realize due to Nintendo wanting to capitalize on their position as market leader. MS and Sony can't allow the U to sell unchallenged and build up a userbase with no hassle, generation fatigue will set in at some point for this gen and people will begin looking to make a jump into the next gen.
To try and oust the market leader using brute force and specs is a risky option in itself because not only are you raising you production costs and costs of development but if people still stick with the market leader's brand you're in trouble. I think Vita has also had an influence here as it's costing Sony money while being dismantled by the competition.







