Bigrich, if you are running a 10,000GPH pump on your setup, that is the recommended size pump for that filter. I hear what you are saying though; any flow through the filter will be effectively filtering the water. But the issue with undersizing the pump is that you will not be able to properly backwash the media.
My understanding of the minimum GPH requirements is to ensure that the pump is powerful enough to backwash the filter media. If the pump is not powerful enough to lift the media inside of the filter unit and agitate it so that the detrius/fish poop is dislodged from it, you will not be able to properly clean/backwash the filter.
If you run a 200GPH pump on that filter, sure, it will work as a filter, but if you attempt to backwash the unit, nothing will happen because the pump is not powerful enough to stir up/agitate the media. It would be like putting a filter sock in your sump that you could never take out to clean.
This is why I say running this filter is overkill...you would need to run a really large pump that will be expensive to run. Those 1HP and 1.5HP pumps would cost me $300+ per month. It sounds like Bigrich has much lower rates than I do, so it's not as big of a deal, but oversizing your filtration can add up to a lot of money, month after month, year after year. Saving a couple hundred bucks by getting a good deal on a large filter isn't that great of a deal if you have to pay an extra several hundred dollars per year to run the thing.