Just a few thoughts to add:
1) Most people buy a car and expect to only keep it for 3-5 years. On this purchase, they spend $$$$! This of course is not the case with everyone, but is true for a good many people. Consider also, how much more people spend on their car than is absolutely necessary for getting from point A to point B. If you look at a custom IEM in this light, then an expected life of only 3-5 years is not completely unreasonable. You're paying for the experience over a period of time.
2) Consider products in general: Many products fail shortly after their warranty period. Many on the other hand do not. In any case, you do the best you can to buy products that you think will last for a certain length of time, and hope for the best.
3) I have a pair of SR60s that crapped out (left driver) very shortly after the 1 year warranty period ended. I have a HD280 Pro that has a very cracked headband... I don't think the life of IEM's are necessarily less than that of regular headphones. I'm sure in either case (headphones or IEMs), there will be many that far surpass their warranty periods, and many that will not. In the case of IEMs, the scare here is that very few have been in the hands of an average consumer (if you can really call us average) for any real length of time. One thing that's really neat about Ultimate Ears is that they are fairly small still and are far more likely to just fix a product even if it's out of warranty than say Sennheiser.
4) Consider how much most of us spend in upgrades...
I'm sure a good number of people here lose more than $1000 in 3-5 years in upgrading, even if they're reselling the items.
These are definately expensive items, and as such, I'm sure we'd all like them to last a lifetime, but expecting them to is a little ridiculous. If the manufacturers are telling us they average 3-5 years, then you need to decide for yourself if the cost is worth the benefit... You'll get 3-5 years of excellent sound (hopefully more) for a certain price. If that price is too high, don't buy.