You pretty much answered that question to yourself. Yes, the system stores each vote for a node, which involves the storage of IDs of the monks that voted for it. I guess there isn't an index on that, so gathering a monk's voting history would put some load on the database; and creating an index wouldn't improve neither performance nor storage of PerlMonks, either.

If we were to create such a think, to what end would that be? Tell a use case.