It did. I think Unity made ability to compile apps in NaCl, and they switched AngryBots demo to NaCl. I guess that's their answer to linux support.
Maybe some page source code will clarify things:
page html: http://pastebin.com/G19kaznr
1. Yes, NaCl support will be free, just like the normal web player. It is presented as on option on the Web Player build, because the two are very much related. The NaCl player basically plays back the same .unity3d files as the Web Player, when you make a NaCl build, it will generate two html files, one for play back with NaCl and one for playback with the web player.