One should also know that representatives (such as in a parliament, senate or whatever) are not immune to bullying (or bribery) either.
One can also note that some ID providers, like Facebook, actively tries to prevent fake accounts. (According to this link 1.5 percent of Facebook-accounts are fakes). (Other sources have said between 5 and 10 percent).
As OAuth is an open standard, one could assume that more actors becomes "Id providers", not only companies but also different communities (nations, municipalities, associations...).
On the fake-vote issue one should also mention the filtering mechanism (see the demos below), which helps any reviewer of the voting result to see how the voting result varies through the population. Which in turn makes it more difficult for those who wants to sabotage the result. One can for example filter out votes of a certain town, country or school (all depending on how much extra information one extracts from the ID provider).
With for example half a million voters it takes about eight seconds to load the page (do all the database queries). (If the server runs on my computer like mine (Intel core i3))
To speed up page loading, one can make snapshots of the userTab like every day.
This means that the first person who loads the page (or uses a certain set of filters) will experience a slow page load (like above). Those people that loads the page after that or uses filter combinations that anyone else have used, will get a very fast response.