Hi Thomas.
Thanks for raising this. I'm not sure people are cheating in this way but we'll audit the accounts that have been established recently for proper email addresses.
I think what you are seeing is a function of competition promotions. Entries are posted to twitter and competition updates are emailed out to clients who are not yet community members, so that will drive registrations and then voting.
It may surprise you to know that typically fewer than 5% of community members will contribute to discussions and groups in a community, so it's typical to see many people with low/no activity. Voting is a nice way too to encourage people to dip their toe in the water, perhaps so they become more comfortable with other types of participation.