Yeah, a whole half step! He didn't mean E flat tuning, he meant like C and B and even lower tunings then that. I was recording a song in C tuning and it's just almost impossible to hear the bass drum without that click and what sound there is just doesn't have any attack whatsoever. It's also about fast double bass drumming, you wouldn't believe how when you start to get the speed up on double bass pedalling you can just loose all definition if your bass drum isn't tuned right. Just listen to one, the "click" is the only thing you can hear because the rest of the sound is just not fast enough to keep up with that double bass pedalling. Also the other problem is that if you still have that boom sound, when you start to play fast your poor bass player just gets completely lost in the mix. So if you have an old school bass drum you just end up in a recording with a bass drum with no attack and just a completely boomy sound at the bottom of the mix drowning out the bass guitar. It sounds terrible, trust me.
At the end of the day it's a bass DRUM and when you're talking about modern types of lower tuned/fast metal with lots of fast double bass, the DRUM definetly takes precidence over the BASS.