Also this by Dan Didio:
“We’re finding diminishing returns on the books with numbering on spines-they take the same periodical cadence that comes with our regular books. Every subsequent number drops precipitously. The longer those numbers run, the lower and lower those print runs become. Also, I want to make sure we’re clear about what’s in that book. That’s why the title’s more important. I’d like someone to pick it up for the reading experience rather than straight numbering.”
Very depressing. Dan Didio sounds like Tom Brevoort several years ago when people were asking for further Omnibus volumes of Amazing Spider-Man. Basically, he doesn't care about the main buyers of these collections or that numbering has much to do with it. If we go by his thinking, we shouldn't buy Flash by Johns Vol. 1 because we don't know if we'll even get Vol. 2 or 3.