I had heard a loooooong time ago that the HDD was 8 GB.
That's because the original specs of the XBOX had the HD at 8GB. Then is was later upped to 10GB...where it has been for more than half year or so (I guess you missed this period). Then, recently, it was learned that is was decided to go back with the 8GB HD. I heard this was due to a couple different companies bidding on being the supplier of HDs for the XBOX. Then, apparently, the company offering the 8GB drives won the bidding.
Aaron