Makes sense to me actually. I can't imagine having a grain bill that would fall low enough for me to ever worry about it. Use to be we said don't use too many non-fermentable grains/adjuncts or you may not achieve conversion. In the case of wheat beers I used 60/40 barley/wheat as a guideline.
Looks to me like you would never use enough of the example grains listed to get anywhere near 30°L. Am I correct in that assumption?