The only time that I have replaced rims was because of brake wear and those replacements are infrequent. If your rim are consistently cracking at the spoke eyelets it is definitely likely that they have been over-tensioned. Doing a 30 day adjustment on a properly built wheel is unnecessary unless there is a clear issue. Find yourself another mechanic.

Of course if you can crank out power like Erik Zabel, that could be the the cause.