Their sales definitely fueled it, though the fact that it was a cheaper way to print for self-publishing and small press start-ups had more to do with it.  Cerebus was already successful, pointing the way towards black & white being a viable publishing format; to say nothing of Warren and the Marvel magazines.  The speculating on new black & white comics was definitely down to the Turtles.

You see this again and again, with the evolution of the specialty shops and direct market.  People speculate of a first issue and sales are way higher than they have a right to be and everyone jumps on the bandwagon.  Then, everyone starts losing their shirt on bad investments.  In the 70s, It was Shazam #1 and Sandman #1, followed by Howard the Duck #1.  The Direct Market wasn't yet the all-powerful force; but, it is dealer/collector speculation driving the surprise sales.  Later, it is the direct market, though it's the same kinds of dealers and collectors.  You see it with the Turtles spawning fevered buying of new black & white titles, until you see comic shops giving away the things, because they went nuts.  Then it is Image and the launches of The Ultraverse and Comics Greatest World and similar start-ups.  You also see it with some self-publishing, thanks to the boost Bone got from Cerebus.  The 90s was when it all came to a head, with dozens of new start-ups playing to the speculator mentality, while the mainstream companies pushed gimmicks and special issues at it.  The end result is a ton of #$%^, more than the usual levels of excrement.  Comic dealers start going under because they blew all of their cash on junk they can't return and can't sell and speculators who got burnt left the market.  Marvel's Heroes World debacle was just icing on the cake, though that helped kill good publishers, as well as the con artists.