I agree with your opinion on the extra "functionality" added by the physics, it doesn't hinder the experience at all (like scripted evvents, imo, totally take away the action and spontaneity of the game). Using it for certain set purposes or goals is great, but I think things shouldn't be made all too scripted or obligatory. HL2 does really well in this regard and that's why everybody likes it so much of course.
To explain a bit more: I really really disliked Call of Duty, because the whole game was scripted to a literal death. And that game was GOTY 2003? I don't believe it! Even a game like doom3, despised by so many on these boards offered 500% more gameplay and applicable intuition to the gamer than the whole "oh yeah, and then the player comes in and points his gun somewhere, shoots, and the scripting continues"-approach of that bogus movie-like pile of crap. I thought the days of CDi were over.