As far as I can tell, it's luck. All totalled I've owned about 16 modules over the past 4 years. That's about 11 lamp modules, 2 wall switches, 2 outdoor lighting modules, and one RF receiver. Two lamp modules died completely for no apparent reason after a month or two. Aside from that I've had good luck. We did have to replace one wall switch in my parent's house, which may have been due to a serious power surge, but there are pretty big issues with the power on my parents' street.

Anyway, I love the stuff. You can buy modules from higher-quality companies, but it's been more cost-effective for me to buy everything as cheap as possible and simply replace the bad units. All of mine are X10 and RCA brand.