But it looks like it isn't calculated this way, otherwise everyone would have at least the same number of 10-Merit votes as he has 250-Merit votes, so I assume every account can only vote one time for another account either it's 250 Merit or 10 Merit.
I assumed theymos used some overlap: you must be trusted by 10 users with 10+ Merit, and 2 users with 250+ Merit. If you're trusted by 8 users with exactly 10 Merit, and 2 users with exactly 250 Merit, you're also trusted by 10 users with 10+ Merit, so that should be enough.