That may be true at the 10G level (which I didn't price), but isn't true (in my experience) at 1G. Plus, it's a lot more likely that you'd want 10G of transit and 1G of comcast than 1G transit/10G comcast, so per-G, your decent quality (Level(3), nLayer, etc.) transit is going to be cheaper. Comcast also seems to negotiate less, since they're effectively a monopoly on routes to themselves, vs. transit.

(Obviously the right thing to do is grow to needing 10G of comcast and 50-100G of transit...)