Yeah that's a good idea. As time progresses we are going to see more and more abandoned accounts. Their votes definitely shouldn't count.

Regarding the 10 thing, I just saw a post by someone suggesting the amount should be 8, so that a large account can't split its SP between two accounts and potentially get a supermajority for centralised control. With 8 votes, a large account can only get 16 witness at maximum by splitting their SP 50:50. Would have to do some maths to work out whether a huge account could still vote top 20 if it split its SP in three.