Valve done this of their own accord, Sierra knew nothing about it till last minute. Had a conversation with someone at Sierra when i purchased HL2 about not having a net connection at the time and not being happy about the way valve had done it and was told that valve would not be releasing anything else via Sierra.
Guy at Sierra was great, even offered a full refund on the game if I wasnt getting the net installed, very helpful and pleasant to talk to.
Personally I will not buy anymore valve games at all regardless of what they are (next big thing or not) but will continue to purchase games from Sierra