Actually, I don't think documentation...
Actually, I don't think documentation of existing RAW formats is enough!
This is basically the same problem we see in other parts of the computer industry where vendors want to lock their customers into their proprietary formats. I bought the camera, I took the picture, I OWN BOTH! Why then can't I do whatever I please with it?
If I choose to write my own converting software to convert MY images from MY camera the manufacturer shouldn't be hindering me!
And since I use linux, I can't use the manufacturers software anyway.
Open standards are a necessity of a free society, and camera RAW files are no exception.
Adobe has already developed the DNG format, so camera manufacturers don't even have to get together to create anything new!
As I see it it would be CHEAPER for a manufacturer to take an existing format and use it than to design yet another and having to build yet newer tools to support it.
Only reason I can find is that they want to milk their customers for every last penny they can pry away by offering "better" and "better" to higher and higher prices.
I know of only two objections that camera makers might raise...
I know of only two objections that camera makers might raise against using a common raw format:
1. The first time they use it, it would cost them more effort than just making modifications to formats they already use. There is a "learning curve". After that, as you say, it should be cheaper.
2. They would be unable to use encryption to "lock in" their users to their own software. But only Nikon appears to have wanted that, and they have now ageed to provide a mini-SDK just to decrypt the D2X WB, so perhaps they no longer intend to use "lock in".
Leica saved costs with their DMR back. Instead of developing their own software, they supply Photoshop Elements with the DMR back. As you point out.
If camera makers used a common raw format for their cameras, then if they DO provide software, that software would read that format. If they sell that software, they could sell it to the users of OTHER cameras, and make extra money! (If it is good enough! If it isn't, perhaps they should get out of the software business).
Where a photographer already has chosen software tools, surely that photographer must wait, after the maker releases a new camera, for that software to support the new camera, before being able to buy it. If the camera uses a common raw format supported by those tools, then the photographer can buy the camera on "day one". Perhaps that is most important for top-end cameras, which is perhaps why Leica and Hasselblad-Imacon are in the lead with this.
What we need is documentation of existing formats, and use of a common raw format in future. That is more or less what the OpenRAW letter asks for.
Plus a variety of tools to convert with high quality from the existing formats to the common raw format, for those who want to standardise on that format. Open source tools, able to run in Linux as well, would be good. There is a SourceForge project defined, but little progress on it.