What's the difference? In either scenario, you are rewarded proportionately to how much effort you put into landing one large deal or multiple small deals.

"My thought is that, just like in every other aspect of the business, your top players will be your highest paid as part of the normal compensation process--and those top people should be the ones closing the bigger deals. Just because you don't get cut a check for that specific deal doesn't mean there wouldn't be rewards for doing so."

I suspect commissions simply originated from sales reps demanding recognition for their efforts. Bonus structures and salary positioning through systems like FogCreek assume you have fair and competent managers who recognize and reward effort. Sales teams may not always present this luxury, so reps may simply demand these commissions to cover their bases.