I guess I'll address this here.
5MB is tiny.  10MB is.. also tiny.  Going from the size of 1 .mp3 to 2 .mp3s does not bother me as a user in the slightest.
From a programmer's perspective, yes, I wish I could pare down the size of pulling in the svnkit library.  It's possible that I may do so in the future.  If I'm not able to, I will lose exactly zero sleep over it.  I consider this feature easily important enough to justify increasing the .jar by that much or more.
If you're curious, half of the size comes from precompiled libraries - one to allow java to run native code, one to allow java to interface with SQL databases, one to handle SSH, etc.  Altogether I refute the claim, though, that mafia only uses a "fraction" of what svnkit provides - just svn update is probably capable of accessing 25-30% of the codebase alone, maybe more.  It doesn't normally, sure, but people can do a lot of advanced things to their working copies and svn needs to be able to handle all of those things.  I am happily already using the feature of it merging my local modifications into repo updates, for example.  I think it is fantastic that I do not need to write any additional code to support this or any of the more esoteric svn features; they just work.