I've been in contact with Erin & he will be adding Box2D.XNA to the Google repository shortly. I didn't realize it had been moved, so we'll have to update to the most recent changes. I want it in the same repository because I hate it when ports are scattered everywhere. I would rather our users come to these forums & get the code from the same spot.
The reason we did a 'fresh' port rather than modifying an existing port was because it was easier. In the past we used Box2DX and spent a lot of time making it run fast (for the record, we sent ihar3d a patch...), but it wasn't kept up to date with the latest changes and it was just easier to start fresh than try to figure out how to bring it up to the latest rev.
Once you get over a year behind, you would basically have to go line by line to update it, so starting fresh makes sense. It only took a few days to do (although tedious), so I think it worked out the way we planned. I'm also much more familar with the code now