Also, if you were going to prime the keg with sugar - you use less due to the difference in headspace in the keg vs bottles. Usually 1/3 cup is about all that's needed to carbonate it.
Huh?? Unless you are knocking out lots of CO2 during the bottling process, it should take exactly the same amount of sugar to carb a keg as bottles. It takes the same number of molecules of CO2 to get beer to a given volume of CO2 disolved. Now, temperature during fermentation and bottling make a difference. A lager should take much less sugar than an ale, due to the larger amount of fermentation-derived CO2 in the beer at a colder temperature.
The head space might make a teeny tiny difference, but it shouldn't make much.
I always read that and assumed it was differences in headspace, but not that I calculated it there probably isn't much of a difference. I have read to use less sugar to carbonate kegs than bottles though. Hmm.