I think tablets/smart phones have shown that most people are happy with 'good enough'.
I have to strongly disagree. They're only "good enough" for their form factor, and for a short period of time. Nobody expects to be playing Crysis 3 on a tablet any time soon. But if one manufacturer released such a tablet, while still achieving good battery life and not costing a kidney, it would sell better than the competition's tablets.
Don't forget that we actually get used to higher performance really quickly. If you've used an iPhone 4S for a while, and then for some reason have to switch back to an iPhone 4, it feels noticeably slower. So it's only what you've experienced before that determines what is "good enough".
Mobile chip manufacturers are pushing the limits really hard, because speed sells. The CPU rating is often the first thing you see below the picture of a mobile phone in an advertisement. It would be unacceptable to have a single-core or less than 1 GHz, even though that was "good enough" just a year ago!
We also typically replace or phones more often than our desktop PC, which means that while each generation of phone is only slightly faster than the previous one, over the course of several years they've become way faster!
And as mentioned above, the desktop/laptop market is temporarily stagnating due to a lack in the ability to easily extract all the performance offered by modern CPUs. This will change dramatically with Haswell, which has an instruction set suitable for SPMD (read: easy vectorization), and TSX for efficient multi-core scaling. Once applications make use of these capabilities, you'll want to upgrade to keep up.