Why does git-svn dcommit rewrite the log messages?

I see that it appends text to the log messages with the SVN repository
revision and ID.  Does it do that because:

1) That's the _only_ way to keep git & svn in sync
If so, then I guess I'm out of luck.  But it seems (to my
inexperienced eye) to make branching impossible in git -- as soon as I
do a "git-svn dcommit", I lose the commit on which my branch was
originally based.  Or, am I missing something?

2) That was the simplest way to keep them in sync at the time git-svn
was written and it hasn't bothered anybody enough to go back and fix
it.
If so, I'd be glad to see what I could do to fix it.  I would also
appreciate any pointers folks might care to give to get me started.

--wpd