You know, there's a lot of organizations that REQUIRE YOU TO RE-REGISTER to remain active - sometimes yearly, sometimes every other year.
My kids have to have a physical done every year to remain in county sports - my son, in Special Olymmpics - every other year.
Your CAR'S registration must be updated every other year - or it's no good. Ok, with that one you also have to pay a fee, while the others are more or less "free".
I think you should have to re-register to vote EVERY ELECTION CYCLE. Make it easy enough, but make it a requirement.
I don't know of anything else where you're good after having registered ONE TIME.