I don’t see why you shouldn’t be able to for your own topic. By not voting for your own topic, doesn’t that seem like you’re not sure if it is good? Even politicians vote for themselves. 
If you have an even number of people vote on a topic (without you voting) and it comes out a tie, then your own vote would be the tie-breaker. JMHO.
Why should only other users be allowed to vote on your topic and be allowed to vote on their own, and you can’t? This sounds like you’re penalizing yourself because you are a Mod or Admin. Doesn’t sound fair to you.