I agree. Mechanistically, I'd speculate that +1's follow and reinforce pre-existing web rankings. It seems very probable to me that people are most likely to +1

I agree. Mechanistically, I'd speculate that +1's follow and reinforce pre-existing web rankings. It seems very probable to me that people are most likely to +1 the pages that are found first in web searches (i.e. those that have high rank).