One more thing I thought of in the shower: the reasons to not go to a 48/38/28 are that it is, again, a triple, with poorer (even if marginally) shifting. It wouldn't make much sense to go with a 48/38, either, because you're sacrificing much of your top speed (more than a 50/something compact, even). That's fine if you're touring, but most of us are straight road riders, and want some zip. Dropping to a compact lets us have a 50, or 48, big ring, and a small ring that's reasonable for climbing even with a closer-spaced cassette (witness the 12-25 vs 12-27 difference above).