Those are the maximum limits on submissions. We wanted to keep the Professional version really high so that you wouldn't have to worry about filling your quota. That's why we set such a high limit.
We only listen our users and don't like to look at similar services since JotForm is very different and innovative, but one thing we looked at was to pricing for similar services and we made sure that our pricing is the best deal. Our price/benefit ratio is best on all versions including the Free, Premium and Professional. It may sound cliche but I really believe we have the best product and the lowest prices.