From what I have seen, Gary's participation in online forums was a personal pleasure -- both for him, and for us fans. Certainly nothing WotC did had a thing to do with my sharing of his interest in the English language (and puns in particular)!
As to debts ...
Gygax created D&D and TSR, and D&D and TSR created the RPG industry. The influence of D&D in particular on the proliferation of similar heroic fantasy tropes and game assumptions in other media paved the way for the success of Magic: The Gathering.
Losing control of his creations was business. Getting paid for his work as an employee of TSR was business. TSR's costly settlement with GDW to quash Gary's Dangerous Journeys game was business. WotC publishing (and outright purchasing?) his articles was business. The Swords & Sorcery and Troll Lord Games deals, like those with other book publishers before, were business.
The products of his work are worth money in their own right, and so is the recognition of his name. I don't see that WotC did him any greater favor than he did WotC.
I don't see how the eagerness of people to interact with him at Dragonsfoot had anything to do with WotC. Such eagerness at ENworld almost certainly contributed more to sales of WotC product than to sales of his own Lejendary Adventures game!
The reason Dragonsfoot had a lot of traffic in the first place was the continuing popularity of his most famous creation. The reason WotC's D&D and ENworld existed in the first place seems to me because of brand loyalty to the name of his most famous creation.
People didn't flock to converse with him because he was just some shmoe who happened to be one of a zillion posters at a big Web site. I reckon this very thread owes its popularity so far to the name of Gygax -- not to the name of Bullgrit!
If Gary had instead posted as regularly at more obscure D&D-oriented sites, linked (via, e.g., Google) to the likes of Dragonsfoot, I am sure they would not long have remained so obscure.
If he had been able to publish his game as Gary Gygax's Dungeons & Dragons, then where do you think a competitor from WotC would be?
Even WotC itself was not exactly selling 4e on the basis of how great 3e was. There's apparently a big "value added" in association with D&D "intellectual properties" going back to Gygax and crew.
Even the term "Armor Class", which is not trademarked and no longer retains even a shred of its original meaning, goes back to the Chainmail rules set by Gygax and Perren. Not only do a number of spells as well, but even the distinctive spell name "Cloudkill" in 4e. Ditto the various colors of dragons with their special powers.