The most interesting quote from your link above Graham is the last quote from the Adobe man "Adobe publishes the PDF standard in its entirety and makes it available for free, without restrictions, to anyone who cares to use it," Adobe Senior Director of Public Policy Michael Engelhardt wrote. "No one needs permission from Adobe to build their own product with the PDF standard."
So why did Microsoft have to change its plans? Because it wanted to produce something which didn't conform to the pdf standard, yet still call it a pdf. Embrace, enhance, extinguish. Microsoft are rarely the innocent party in these matters, no matter what their PR machine says.
Colin