Biggest two reasons for heater failure are: getting too small a heater for the tank, or else dropping something onto it and shattering the glass.
If the heater is on too much of the time, it can jam, and then it overheats, and then it cracks. One approach taken by the professionals is to use two, slightly underpowered heaters. These work in tandem, with neither on too much of the time, and so helping each heater last for much longer. When both are on, they warm the tank up easily, but if one fails in the on position, it isn't big enough to overheat the tank. If it tails in the off position, the remaining heater will keep the tank from getting too cold, so keeping the fish alive, if not actually happy, until the aquarist notices the problem.
As for breaking heaters, always make sure the heater is well away from rocks, bogwood, etc. If you are keeping big fish, consider getting a heater guard, or better yet, a filter with a built-in heater (as is the case with Jewel tanks).
Heaters are one place not to economise. If they fail, it's a disaster, and they can fail explosively, sending shards of glass into the tank, which are very difficult to see underwater.
Used properly, good heaters last for years and years. Five years doesn't surprise me in the least. The Jewel ones seem very good, and I certainly know of a couple of people with such systems that are seven or eight years old.
Cheers,
Neale