You are correct, the paper does not compare to compression with a null prefix. In haste I read it wrong, since it was not too far off from calculations I had done previously in a reddit discussion where I found ~100 bytes saved using the prefix dictionary. Thanks for being persistent and I'll see if I can rerun their data using a null prefix before the next Spdy thread, but I doubt it will show more than 200 bytes total savings per connection, which doesn't change anything IMO.