I understand D&D is the "Windows" of RPGs. I understand the market- and mind-share it enjoys. (Those movies: not many people remember or know about them though!). Obviously when Paizo forked D&D 3.5 and started Pathfinder, they were riding on the popularity of this particular RPG. Also evident is why there is a cottage industry of third-party modules, campaigns and gadgets for D&D: it makes sense to make these for the most popular system.

The thing is, it's much harder to implement "vendor lock-in" for RPGs than it is for hardware or software which has business uses. The cost of switching to another RPG system is very low: all it takes for a group of friends to start a new RPG is for the geekiest of them to buy a rulebook and evangelize it, there's almost zero cost (but the rulebook(s), of course).

I find videogames are a red herring as an argument for D&D, since most people playing CRPGs based on D&D don't even need to understand the rules; the computer does everything for them. And people will buy a flashy CRPG regardless of the underlying engine, all that matters is that the game is fun, hyped, has nice graphics, and friends are playing.