Only 2 SD-Cards in 3 years? You are lucky.
It is not a matter of unclean shutdown, powerloss, bad power supply or wear leveling, but in many cases the Raspberry Pi eats SD-Cards which are fresh and new after a short while (in may case the file system git corrupted in the process of the firts apt-get update after installing the OS image.
The best one can do is exactly moving to usb sticks or usb harddisks.
Do you have scientific proof for that? 
As I said in my linked comment, of course SD cards can fail eventually. But you should look at the hard evidence: 48 MByte/h - that’s the write rate I saw in mean over the course of one week on my productive system. Do the math. Everything else depends on the sd card product you are using and the steady operating environment.
Yes, I (and others) have:
To be fair, the developers of the raspberry firmware did their best to improve the SD-Card handling.
But what I understood was, that they handle different SD-Card differently. Some operation like ERASE, which is leggit on all cards, improve performance on some while loose information on others leading to corrupted file systems.
Allways update your raspberry pi firmware to the latest.
If you follow the advice to buy some supported cards you are ‘only’ affected by wear leveling.