I am not a vc user.  I find magit far more helpful.

That said I took a look at vc.el.  Interestingly it has a
vc-checkin command but neither vc-push nor vc-commit.  From
this I surmise that at the time vc.el acquired support for
the DVCS model the choice was made to map vc-checkin to the
local commit operation and leave it to the DCVS backends to
provide a command to push to the central repository.

Though too much water may have flowed under the bridge to
revisit that choice it seems to me an alternative would have
been to preserve vc-checkin as the command that pushed one's
work to the central repository, leaving it to DCVS backends
to support the new concept of committing locally.

/john