Comment 8 for bug 52711

As I've said in https://bugs.edge.launchpad.net/ubuntu/+source/git-core/+bug/178603/comments/2 already (and as the Debian bug states):

Fetching through http is just one part of git core, and not necessarily used by all users. That's why the git-core package Recommends: curl, most of it works just fine without curl being installed.

That's what Recommends is meant for and the error message in case of failure is clear enough IMHO:
  /usr/bin/git-clone: 356: curl: not found

The most common way to use git is the git protocol itself, and for this curl isn't required.