The link you cited from nhtsa.dot.gov actually said it was 29% of fatalities, and that was only for BAC of 0.08 or higher. I'm not sure it's tracked anywhere, but I'd be surprised if there weren't a lot more where the BAC didn't rise to that level, but was still a factor. I agree that steeper penalties may not help though.
Thanks for pointing that out. I'm not sure how to reconcile the 29% listed in the intro and table 4, with the 20% listed in table 2 and table 3.
Table 4 shows BAC >0.01 if you are interested.