I'm pretty sure there is a competing botnet that would be happy to override votes of your botnet. If online votes are counted only once, then what matters is which botnet is faster and has a better link to the voting servers. High Frequency Voting, in other words.
Haha, you’re right! So, as always, it boils down to an arms race between the two sides. So keep an eye on who's leasing office space near the voting server data centers.