Yep, the demand for upvotes is currently far greater than the supply. Probably because STEEM price is higher than STEEM feed price which means that it's very profitable to buy votes now because in few days the upvotes will be worth more.
Anyway in few days the demand/supply should be more balanced and @tipU voting service should be available for longer each day.
Ok, thanks for the explanation. I guess I should be trying hard to get some votes in from places because of the supply issue.