Well they can always do the same thing by creating pages that do such things. Link to a bunch of tech sites, then put a link to the dating site.
Google is very good at detecting this sort of insincere promotion, and compensating for it. That's probably the the hardest problem, and the one most core to its business, that Google addresses. For someone to actually game the system, they end up having to work pretty hard to make good content and appear sincere, and in the end, they might actually be making a more positive than negative impact.
I see no reason why Google can't apply the same expertise they apply to links on pages, to +1's. The nice thing is that they end up with so much more data, that it becomes even harder to game it because each individual has such a tiny influence.