Ok, this thought I'll admit is way out in conspiracy theory land, but here goes. What if a reason Google is withholding Honeycomb source is due to them not wanting to have to compete with Amazon? There has been a lot of speculation recently that Amazon may look to build their own tablet to compete with Apple, and potentially the other Android tablets. This tablet could potentially run just the open part of Android, ignoring the proprietary Google parts. Out of the gate, there would still be a place to get apps (Amazon Appstore), a place to stream videos from (Amazon Instant Video), a place to buy music from (Amazon MP3 Store), a place to buy books from (Kindle Store), and a place to stream cloud music from (Amazon Cloud Player).

Amazon would be entering the field with an ecosystem that rivals, or even beats Apple's in certain areas, and also would be stronger then what Google offers today on the media side. Motorola, Samsung, and the other Android tablet makers have next to nothing when looking at ecosystems. This could do severe damage to the already slow start of Android with Google as a tablet platform.