If the lots are adjacent and only one has a house on it, our association charges just one assessment and gives just one vote. We used to have a developer who owned multiple lots. If we had allowed him one vote per lot, he could have had an unfair influence. Also, it was hard enough to get him to pay just one assessment. If we had charged him for each lot, I'm sure he would have put up a fight.
I'd like to hear what other associations have done.