Well color me confused, I didn't realize the Sony was a closed system.
I work elbow to elbow with Amazon folks and I can tell you: for the most part they're pretty smart. The numerous, well documented failings of the hardware had to count for more than the availability of a PDF, xhtml and txt viewers.
Besides, iRex could have easily speed up the iLiad's boot by stripping it down to just a Mobipocket viewer for Amazon.