Having just put a 26/36/46 with 165 cranks onto Terrie's Birthday SXP (shhhh!   ), I now have an "extra" 30/42/52, complete with 175mm cranks.  This got me thinking about gear tooth wear, and the fact that I've replaced two rear XT cassettes on MY SXP over the last couple of years due to chain wear resulting in gears slipping -- but replacing the front triple was never suggested by the LBS.
 
Given 12,000+ miles on my original 30/42/52, should I swap out Charlie's old one (that only had ~4,000 miles on it), and pitch the original, or is a front chainring good for many more miles?  And if so, why isn't wear on the front rings as significant as on the back -- more teeth to engage?
 
Hep me, hep me!