The pot actually called the kettle black, so you posted an image of the wrong object.
He's right though.
"I did it, and it's fine therefore it doesn't exist" is a terrible retort.
WP7.5 had a critical bug where if you use Internet Sharing it bugged your WiFi to the point where your phone would use your data connection even if your WiFi was turned on and connected. People who never used the tethering feature (T-Mobile gave us that for free, they didn't want to pay on their other carriers) chimed in with flames saying we were just trying to trash the platform.
That's what the above sounds like.
Over-Life performance degradation really doesn't exist on any decent PC, which even a cheap eMachines can be considered these days compared to what was being sold in stores 5-6 years ago. Hasn't really been an issue since XP. Vista and 7 solved that for the most part, especially with things like Windows Defender and Microsoft Security Essentials being either built-in or preloaded on so many PCs to stop the real culprits from causing issues.
I haven't had even an Android device (granted I've only really bought high end devices, anyways, not low-mid range but those are spec-competitive with the best blackberries these days anyways) degrade in performance over time, and I certainly haven't had an iOS or Windows Phone device do that.
The only time I expect to factory reset a device is:
1. If I do a major FW upgrade (full OS upgrade i.e. Android GB to ICS or WP7 NoDo to Mango) and the update process doesn't do it itself. This is mostly out of habit, though, but since orphan settings can sometimes cause issues I do it to save myself potential troubleshooting time. I typically don't backup and restore anything as it can restore problem files back onto the device. It's too easy to find and reinstall the apps you need.
2. If the device is broke (software-wise) and doesn't boot properly. In that case, most devices hae a 2-3 HW button method to reset the device.
3. If I'm selling or giving the device to someone else, to make sure all of my information is off of it. The Reset Process can reformat all the storage in one go and restore everything to factory defaults.
I don't reset devices for performance degradation because:
1. I haven't had a PC or device do that in over half a decade and,
2. I would simply return the product or avoid buying it. For example when BB10 launches if I hear anything about devices degrading in performance a few months after launch I would simply not consider it. This is how these things work in the real world.