Dear Geoffrey,
Longevity is dependent on the alloy/heat treatment used for the ring, and the number of teeth. I get around 20K mi out of 7075 heat-treated rings in the 42-48T range, though I change chains pretty aggressively. I replace cogs when they start skipping on a new chain.
I got very little mileage from the VO chainrings <marked> as 7075, but they sure didn't wear (or corrode) like it. I bent the hell out of them before they were completely gone in a crash, but they were getting badly shark-toothed after less than 5,000mi. Even the inner had visible wear!
Some of the Vuelta rings wore fast, too, but all the TA rings, Salsa, the nicest Sugino, Campagnolo (well, 10s Record ones, anyway), and Compass/RH outers last very well. I've got IRD rings on my Allroad right now, and I don't have enough mileage to really assess wear yet on it (3,000mi or so).
I've never worn out an inner/granny ring, even though wear on those should be accelerated relative to the larger rings. I ordinarily gear my bikes such that I don't spend lots of time on that inner ring, except my "racing" bike. There the default 'round town is the inner 42T ring, despite the well known fact that to "go big is already to go fast". Thanks, Paul Fournel.
Cheers,
Will