Camera's are heading to higher and higher pixel counts, so they need sharper lenses.
Lenses should be designed and bought with photographers' needs, rather than sensor specs, in mind.
I very rarely print larger than A4, which means 99.9% of the time I could do with ~8MP at 300DPI + margin for crop, so the current crop of 18MP sensors is already an overkill for me.
I'm not going to complain about rise in sensor resolution, as disks & memory cards are getting larger, faster, and cheaper all the time, but why the hell would I spend money & effort on sharper lenses & better stabilization just to get those extra pixels I don't need to begin with?
I'm sure the multiple benefits of high resolution (like cropping) have been listed a zillion times, so I'll skip that. An ultra-wide has many uses, not the least of which is landscape, and most ultra-wide shots are vastly improved by sharp resolution. It has become a point of pride with some people here that they don't "need" this or that improvement. That's shortsighted in my opinion. Anyone can opt-out of improved technology at any time, and old "good-enough" lenses are always available for you. If you are completely satisfied with what you have, good for you, you'll save money. But the world moves on, and I prefer to move on with it.