What are the actual sales numbers for these titles? As to whether DOA can compete commercially, I think London's very point was that it would face stiffer competition on the PS2, therefore sales would likely be better on the XBox. That doesn't change its commercial success (or lack there of, since we don't have the numbers yet), of course, in terms of sales numbers. A good comparison would be DOA2 Extreme's sales vs Tekkan Tag's (both came out around the same time). Looking at Soul Calipers multiplatform sales might also give some insight into the subject of how competition may effect sales.
EDIT
Ah, I see everyone beat me to the punch. ^^