You're forgetting a couple of things:
1. Resistance 2 is largely aimed towards the 16-30 male demographic, who vote in INCREDIBLY small numbers anyways.
2. It's not like you can't just vote and buy the game in one day. Doesn't the game have a midnight launch anyways?
3. My estimations took about a couple seconds, but Resistance 2 will have about 5 days or so of sales in its first week for Vgchartz data. The first day sales might be slightly affected, but the first week won't be by the slightest percent (unless supply problems come up).
4. If anything, election day will motivate more people to go out of their houses and near schools, malls, and stores. They can pick up Resistance 2 on their way by.