I'm with Chad (and others) on this. If you wanted to reduce the failure rate of your ability to tell time underground, you could always use redundancy and carry a second watch in your pack. Two cheap watches are still cheap compared to one expensive one.
I use a cheap
Casio Illuminator for caving...and everything else. It doesn't have any advanced features, but it tells time (and has an alarm and stopwatch), and is easily read even though heavily scratched. It has never failed me, and it has been beaten up considerably and kept underwater for extended periods of time. I did lose one once when the band broke in a cave. Given the years that I'd had it for, my only regret about that was that I had littered the cave. Then I got out of the cave and put on the other one that I already had, for when I lost the first one around the house.
(Mine has the soft plastic band...I'm sure the metal band shown in the picture would be uncomfortable in a cave, and maybe corrode or tarnish too. I'm just posting a link to Amazon so that people who prefer not to shop at Wal-Mart know they can still get cheap stuff.)
Rather than buy an expensive watch, I'd rather spend more money on just about any other piece of caving equipment.
I do recommend wearing a watch caving...or at least bringing something in the pack that tells time. Or at least having someone in the party with a watch...or if the party is large, two people, so that if the party splits up you have two watches. In addition to the obvious reasons for wanting to be able to tell time in a cave (e.g. how long do we have before we have to leave or trigger an unnecessary rescue? how long has Bob been in that tiny squeeze and should we send someone in to check on him? how long did it take us to do this stretch of cave, so we know for future planning? who climbed up the pit rope the fastest?), a watch is also handy if someone becomes injured. You can send someone out who knows the
time the injury occurred (and in addition to memorizing the time and description of the injury and vital signs, you can also send them out with that information written in pencil or waterproof ink on a piece of paper torn out of your little waterproof notebook that you always bring). Plus, if you want to know how fast someone's heart is beating and how fast they're breathing, it helps to have a watch.