Launchpad supports Bazaar only. That's one of the "top ten reasons" to switch to Bazaar according to the docs [1].

That said, I don't really think Canonical is "forcing" anyone besides playing the "defaults" card in the distribution they control, and even then you can simply not use the stuff is installed by default (although I think that making the desktop dependent of some applications that I may not want to use is a little bit against the bazaar philosophy of Linux distributions).

[1] http://doc.bazaar.canonical.com/migration/en/why-switch-to-b...

EDIT: formatting