Brewing capacity would be a major issue to their bottling also, at least in the short term.
Some quick math, in Honda's 16 Nov 2005 post he stated that the worthouse was at 30% capacity (10 stores being supplied), so roughly 34 stores could be supported at 100%.
We're at 18 stores now, expect another 7-8 in '08 (26) and likely another 7 after that, to hit 34 restaurants.
If GC were to bottle, they'd have to do it now, as they should be planning on having another worthouse online in less than 2 years, just using my fuzzy math.
Bottling would be more feasible in another 2-3 years when the next worthouse is operational, and the chain has grow out off the midwest. By then extra worthouse capacity could be utilized for bottling without taxing the system.