Hmm, there seems to be the implication that we've hit some magical end state in hardware development where consumer needs are forever met.
Personally, I think of these hardware market developments with an eye toward interplay with the software market. Historically, software developers had to consider the capabilities of consumer hardware in determining feature scope and user experience. Hardware capabilities served as a restraint on the product, and ignoring them could effectively reduce market size. The effect was two-sided though, with new more demanding software driving consumers to upgrade. Currently, in this model, the hardware stagnation can be interpreted as mutually-reinforcing conditions of software developers not developing to the limit of current hardware to deliver marketable products, and consumers not feeling the need to upgrade. In a sense, the hardware demands of software have stagnated as well.
From this, I wonder if the stagnation is due to a divergence in the difficulty in developing software that can utilize modern computing power in a way that is useful/marketable from that of advancing hardware. Such a divergence can be attributed to a glut of novice programmers that lack experience in large development efforts and the increasing scarcity and exponential demand for experienced developers. Alternatively, the recent increase in the value of design over raw features could inhibit consideration of raw computing power in product innovation. Another explanation could be that changes to the software market brought about by SaaS, indie development, and app store models seem to promote smaller, simpler end-user software products (e.g. web browsers vs office suites).
I wouldn't be surprised if this stagnation is reversed in the future (5+ years from now) from increased software demands. Areas remain for high-powered consumer hardware, including home servers (an area that has been evolving for some time, with untapped potential in media storage, automation and device integration, as well as resolving increasing privacy concerns of consumer SaaS, community mesh networking and resource pooling, etc), virtual reality, and much more sophisticated, intuitive creative products (programming, motion graphics, 3d modeling, video editing, audio composition, all of which I instinctively feel are ripe for disruption).