Well, they do that already - to a point. Mountain bikes use a wider rear hub spacing to gain an extra 5mm of space and they don't use 10 speed cogsets (yet).
If you're riding a long flat road, it's nice if you can find a gear that's right in the sweet spot. That way you don't feel like you're pedaling too hard or having to spin your feet too fast. I think that a majority of riders appreciate close ratio cogsets.