Haven't read the others yet, but I'll take the plunge.
The BR camp, judging from Sony's reported position, feels that Dual Format players would give "credibility" to HD DVD, since it would be an admission that HD DVD has gotten strong enough in the market to support with new hardware from more vendors.
Second, and this is unstated, I believe that they are VERY worried about hybrid players because the state of play for Bluray hardware is in a mess right now. The standalone players current on sale for Bluray don't have the hardware necessary to meet the 1.1 player profile spec, and so will never be compatible with 1.1 or 2.0.
Furthermore, Bluray players are more expensive than HD DVD players - there are a whole raft of Bluray players at $1,000 SRP and higher, yet most of them do not support a good feature set. So if ANY player were to come along, at the same price, and offer 1080p24, HDMI 1.3, DD+, TrueHD, DTS-HD MA, BD-Video 1.1 compatibility, and so on - it would wipe out these other BR players - The Samsung UP5000 has all of that - AND it plays HD DVDs as well.
The Samsung could DECIMATE the high-end BD player market.
HD DVD is protected from much of this. Their strategy has been to go for the mass market all along, not to profiteer with the traditional adoption model. So they are focussing on players from the $200 mark, up to the $500 mark, with a very complete set of features. And their most expensive player retails (currently) at $799.
Therefore, universal players in the $900 range will supplant Bluray player sales to a greater degree than HD DVD sales.
If the majority of standalone players in the mass market are HD DVD, and the majority of standalone players at the "high end" are hybrids, then studios will see quite clearly that the largest market for their movies is on the HD DVD disc.
This terrifies the everlovin' cr*p out of the Bluray folks, and many of their supporters. Have you noticed in the "intent to buy poll" for the Samsung, almost all the bluray folks said they WOULDN'T buy the Samsung?
However, in the real market, practical folks will choose the Samsung over a standalone BR player, and folks who can't afford both formats are going to pick HD DVD.
I have more detail on this thinking in my Samsung
and LG player