I'm betting any yeast manufacturer would answer your question better than us, most are very nice people
I've been in touch with Imperial, and yes, they seem great people. That was about something else, but I've asked them about this, too, and I'm still hoping for an answer. It's been a few days, but I guess they've got other things to do besides answering questions from me.
Well they are responsible for billions upon billions of lives... no matter how relatively small they are.
I'm not sure John smokes? Anyway, he's not the yeast expert, he's probably got this from Chris White, or at least he has ok'd it. (He's on the acknowledgements list in HtBr.). But I've heard this in a beersmith podcast as well from guys from Imperial Yeast - and they're yeast experts. Link to the pod in my first post.