"It's our firm conviction that at least a sizable portion of the future of comics lies in a larger, more expensive, even more mature product than today's color-comics market is structured to allow. In a day when Playboy and other magazines sell for a buck (and more, on such gala holidays as Christmas, New Year, and Hugh Hefner's birthday)--in a day when a forty- or fifty cent cover price is possible only to a magazine of tremendous initial circulation--in short, in a time of creeping inflation, rampant overcrowding of the newsstands--we felt that, even though Marvel's popularity is at an all-time high, we'd be fools and klutzes not to experiment with other prices, other sizes, other formats."
It's my theory that what Thomas was saying in '73 was by then common wisdom for Marvel since about 1970-71. I've always considered the Bronze Age-- which I place in 1970-- to be a new era because that's when the Big Two took their first faltering steps toward "adult entertainment," as represented by Marvel's CONAN and DC's GREEN LANTERN. I must admit that there's a big marketing difference in the two, since the former was aiming for success based on the popularity of the paperback Howard reprints while the latter was a gamble aimed at keeping a failing book alive. Still, both are predicated on appealing to non-juvenile interests.
That Thomas was thinking in this wise long before 1973 is evinced in the 1971 premiere of SAVAGE TALES, for which Roy is billed as "associate editor." The idea of appealing to an older market would be a logical step since it's commonly asserted that sales in the late 1960s went way down, as the superhero bubble, prompted in part by the BATMAN teleseries, went kerblooey.
Marvel-- which also attempted to corner the underground market with the 1974-76 COMIX BOOK-- seems to have been more heavily invested in developing this market than DC, or even Warren. I've read very little of Silver Age Warren, so I don't know if its horror and war stories were on a par with the more mature stories of EC Comics, nor do I know whether or not the Warren audience skewed older than that of Marvel and DC. Warren did begin VAMPIRELLA in 1969, so that would seem to be a more overt courting of an adult audience by Warren, using sex-and-violence in much the same way Marvel used Conan.
On a side-note, I'd opine that the Marvel guys never seemed to get a handle on adult horror: most of the b&w horror stuff had the same tone as the color comics.
In 1973 it probably made all the sense in the world to assume that magazines would be a secure foundation on which a comics-company could build. For one thing, the company could expect to raise prices when other magazines did, and not lose out, as DC allegedly did when they tried to maintain 25-cent comics against Marvel's 20-centers. But then, who could have predicted that the digital revolution would come close to making all magazine entertainment irrelevant?