Since console hardware is converging towards PCs (as opposed to specialized hardware stratified by make), as well as the expansion of the PC market (which has a massive range of hardware of varying price points and capabilities) the benefits of making a game against the limits of a specific console is less and less of a good idea versus targeting a wide market. If you aren't stuck to exclusivity for a single console, then it makes sense to target previous generation consoles if possible in order to maximize the size of the potential market.