Encourage the same version everywhere (tilde begone)

Given all the issues with fuzzy dependency matching, I'm curious why Bower would want to encourage the use of `~` when installing with `--save`.

I know that npm [set a precedent](https://github.com/isaacs/npm/blob/fc62914b49c540ba364b919ae69b879bdaaec803/lib/install.js#L340-L343) here.  But there's an opportunity to look at the issue with a fresh perspective.

What's the justification for putting `~` in front of versions in `bower.json`?

If performance is a concern (thinking things will be faster by already cached dependencies that ~match-ish), I imagine there could be a bigger gain by avoiding all the excessive git fetching.