The other two Alien games, Alien vs Predator and Aliens: Colonial Marines, an FPS and tactical FPS respectively, are still scheduled for a 2010 release, with the former getting a lot of attention. It was showcased at E3 2009 recently.
I still think part of the reason why the Alien RPG was cancelled was because of other projects on Obsidian's plate, like Fallout: New Vegas, among others. It's a shame, since I would have looked forward to playing it, but it was basically just another vapourware title which was kept on the shelf, gathering dust for years.
Sources:
Obsidian's Aliens RPG Officially Nuked from Orbit
http://www.giantbomb.com/news/obsidians-aliens-rpg-officially-finished/1492/
http://forums.obsidian.net/index.php?showtopic=52620
http://www.shacknews.com/onearticle.x/59150