I, too, love the thin strap and think it wouldn't look right if it were thicker. I think this bag is primarily meant to be carried as a satchel with the messenger strap as an occasional convenience.
I don't know who this model is for sure, though I'm guessing it may be Jackie or Ashley. Being super tall myself, I e-mailed her a similar question about the messenger strap length, and she told me that this bag works great on her (5'5") and another friend (6'0").