Not as rare as you would think, I can think of a ton of games off the top of my head that are near or over ten years old that still receive 3rd party support.
Diablo 2, Starcraft, Total Annihilation, Battlezone 1 and 2, Homeworld 1 and 2, Half-Life, Counter-Strike, as well as a ton of others I probably don't even know about.
I guess I shouldn't say it doesn't matter, it's just that most of the community has given up on it and moved on, where if the company had kept supporting it (like Arcen), people would have been more likely to stay with the promise of official support.