I went back and looked more closely at my spreadsheet. There is a difference in value earned for a Marriott Platinum and a Starwood Platinum (same room rate and number of days). The Marriott Platinum will earn more, but perhaps not so much more as to offset the advantage Starwood provides with no capacity controls.

However, there is a huge difference between Marriott Gold and Starwood Gold. In fact, by my calculations Marriott Gold earns twice the value of Starwood Gold on any given stay. Thus, even if you always had to pay 50% more points to claim an award at Marriott you would still be ahead.

Starwood Basic (2 pts/$) is, of course, much worse. It seems clear that Starwood can afford to offer no capacity controls because the earning potential is so much smaller than the other programs. When comparing Marriott and Starwood, my conclusion is that lack of capacity controls only really benefits Starwood Platinums.