I agree with weirdboy above. There is another factor to consider that I believe may play a role. The headspace in a full keg is going to be significantly less than the combined headspace of 50 bottles of beer. More of the C02 produced is going to be dissolved in the beer in the keg rather than dispersed over the greater headspace in the bottles.
This is just a guess, but it makes sense to me. The nice thing is that if your carbonation comes up short you can easily fix it by force carbonating. Let us know how it turns out.
Primary: Robust Porter from BCS.
Bottled/Kegged: Crappy Bock (my first brew!), IPA, Manny's Octoberfest, Paulaner Hefe-weizen clone (my first all-grain!), Ed's Honey Oatmeal Stout, Dos Equis clone, Pumpkin Spice Ale (my first ruined batch), American Red Ale, Angel Wings from BCS, Edworts Apfelwein, American Wheat from BCS,Terrapin Rye Pale Ale from CYBI, Munich Madness from BCS.