blowing up the vents that zombies pop out of

I was ecstatic to find that you can throw grenades into the vents that zombies crawl out of on various maps. Then I was mildly disappointed, wondering why I went through the effort.
I feel like HE grenades should be able to collapse sewers and such, at least temporarily, when they're tossed inside. I think that would add an additional incentive to play as commando, as well as just being cool.

blowing up the vents that zombies pop out of