I'm not sure what number of Helpful votes is required to mark a thread a helpful, but I think it is too many. If you search a typical forum for helpful threads, the only ones that come up are very old threads with many replies in them.
Despite the fact that voting helpful is more discoverable than before, this option is not often chosen. At least I don't think so -- it's not so easy to tell, because filtering by helpful shows so few entries.
I really don't see why just one helpful vote should not cause the thread to marked as helpful.
[On the other hand, a single Propose as answer (a useless feature) is enough to get the thread marked with Propose as answer.
Similarly for Has Code (another useless feature, partly because the code editor is so bad that I ,for one, never use it).]
