Another update was pushed out today, and this one makes changes to the ending of the game. Here's the new ending. Keep in mind that by watching this, you'll be seeing the end of Portal. The very end. If you don't want to see the end of Portal, don't watch this video, is what I'm saying. Portal ending ahoy. Watch out for "spoilers," if you "catch" my "drift."
The bit about assuming the correct party escort submission position and the part where a robot or something drags you away is new, by the way.
I'm no super-sleuth, but I feel like I can say with some authority that Valve is up to something. Maybe it's a Portal sequel, maybe it's Episode 3, maybe Episode 3 is the Portal sequel, maybe getting all the radios and then beating the game unlocks the Borealis for use in TF2, or maybe they just got really unsatisfied with the ending in Portal and decided to shake it up for no reason whatsoever!
OK, it's probably not that. One thing I will say, though, is that it's kind of neat to use Steam's automatic patching to push sneaky stuff like this out to players.
Seriously, though, I hope they finally bridge the two stories together (HL and Portal).