Jon Austin , Apr 02, 2007; 04:39 p.m.
Compare size and construction: the 30D is larger and has a magnesium alloy "skeleton." Plus the very useful Quick Control Dial.
It's mostly a case of superior interface (30D) vs. newer technology (XTi).
That the 30D wasn't superceded last month by a newer model (a la 40D) with the more current technologies found in the XTi is a source of chagrin and anguish for many Canon 10/20/30D and Digital Rebel (original/XT) owners.