Gamma World vs Traveller

I've been meaning to write a few posts about the more interesting TSR historical tidbits I've gleaned from Polyhedron's interview series. While re-reading the interview of James M. Ward from issue #3, I came across this:

Since this interview came out in late 1981, I assume that Ward's claim about the relative sales figures of the Gamma World and Traveller is based on then-current information. While we don't, so far as I know, have any hard data on TSR's sales of Gamma World, we do know a lot about GDW's sales of Traveller. In 1981, the period about which I assume Ward is talking, GDW sold just shy of 60,000 copies of Traveller for the entire year, or roughly 5000 copies a month. If Ward's assertion above is accurate, Gamma World was doing better than that, though there's no way to know how much better.
Interestingly, Ward later notes, somewhat enviously, that Traveller "has lots of people writing supplements for it," which he implies is the reason for its being more well known. He may be on to something, because, if you look at GDW's sales of its support products for Traveller, they're quite impressive. In 1981 alone, GDW sold 81,159 copies of supplements, like The Spinward Marches and 50,865 copies of adventures, like The Kinunir. Taken together, that's more than twice the number of copies of rulesets sold during the same period (and I'm not including the sales of rules expansion books like Mercenary  or double adventures). 
Ward seems to be aware of the fact that the lack of support for Gamma World – something I regularly note when I talk about the game – had an adverse effect on its popularity relative to other science fiction RPGs of the time. He adds that "only Gary Gygax and myself are writing GAMMA WORLD things," which suggests to me that TSR never had any kind of plan for supporting the game beyond whatever Gygax and others might produce on their own. Of course, I'm left wondering what became of these Gamma World supplements or adventures Ward was supposedly working, because, so far as I know, none of them ever came to publication. 
Without verifiable figures, it's impossible to judge the veracity of the claim that Gamma World outsold Traveller on a monthly basis. I certainly think it's plausible, given the popularity of Dungeons & Dragons at the time and the reach of TSR within the hobby. If Ward is indeed correct, then it represents an incredible misstep on the part of TSR that Gamma World was not better supported, because it would have given them another significant source of revenue at the height of the early '80s RPG fad – but then no one has ever claimed that TSR was the most well run of companies at any point in its existence ...