Confused, why? Something like a pump that runs 24/7/365 is going to fail at some point, usually randomly if there are no issues with your source power & everything is hooked up safely. In your case you had them fail within a rather short time frame, while you were home (which is a good thing, rejoice).
We tend to plug stuff in & trust that it will be fine for years without taking a bit of time to check the components out periodically by shutting them down & having a look at their condition. Since you have the electrical expertise, why not get a meter or power monitor (kill-a-watt) & compare the wattage measured to the wattage rating of your pumps. If there's a significant variance between measured & rated values, might be time to investigate further. Even without extensive electrical training, monitors such as the kill-a-watt are available from most reno/hardware stores for $25 or so. These allow you to monitor the voltage, current or wattage of an electrical device plugged into it. Most of them will also allow you to input your kw/hr cost & tell you approximately what the device hooked up to it is costing you. It's not going to solve all your problems & troubleshoot for you, but it's a worthwhile gadget to have around your home, not just for your fish tank. With the installation of smart meters in most areas of the country, power usage & quality monitoring becomes simpler & more devices are now available to take advantage of the new technology.
http://en.wikipedia.org/wiki/Kill_A_Watt
& you can take things a step further with something like this:
http://en.wikipedia.org/wiki/Home_energy_monitor
or go all out with one of these..
http://electroind.calls.net/?url=htt...ID=DrivenLocal
Alas, despite routine monitoring & scheduled maintenance, there will always be those rogue components that decide to fail at the most inopportune time. That's how it goes with sealed dynamic components that you can't see inside. Again, be happy you were home when the items decided to cook, so you
did catch a break!