Note that if we only take de number of votes as the parameter to determine the awarded address the voting system can also be cheated. Just by distributing the coins over diferent addresses the 'big holder' could emulate serveral users. The point of my proposal is to make the voting system probabilistic: a grant address has more probability of being awarded as more coins (or votes, or a combination of both) support it, so, in the long run, all the grant addresses are awarded proportional to the support they receive. All the nodes in the network should use the same pseudo-random number generator or whatever algorithm to choose the 'winner' address.
Yes, any attempt to enforce a 'number of votes' rather than the 'size of votes' will lead to the gaming the voting.
On the other point - I think have a winner whose likelihood is based on the size of the vote is probably technically possible, but I think it would certainly lead to everyone immediately voting for themselves in the hope of winning.