Off the top of my head one reason would be the Warner insider who was communicating with Mark, one of the mods on here. This fella talked about all sorts of things concerning WBs efforts for BD, and the Samsung unit they were using for compatability testing. His other statements have all turned out to be true (size and power usage of the Samsung, inital MPEG2 WB releases, etc) so there's every reason to believe him when he said WB would be using VC-1 for all subsequent releases after the initial wave of MPEG2 BDs. Throw in the comments Keith has made regarding compatability testing for his company's chips - with discs authored with next gen codecs - and it seems highly likely discs encoded with these codecs will be out fairly soon.
Why haven't companies publicly announced they'll be utilizing new codecs soon? Probably for the same reason Toshiba has made no public announcement of a 2nd gen player! Don't want to undercut what's already on the market.