Why Does Wireless Gear Degrade Over Time?

I saw this originally posted on slashdot, but their comment format is not conducive to actually getting a correct answer.

Having directly experienced this phenomenon myself, I'm now asking here where I think I can actually get an educated answer.

Here's the original question verbatim:

Lately I have replaced several home wireless routers because the signal strength has been found to be degraded. These devices, when new (2+ years ago) would cover an entire house. Over the years, the strength seems to decrease to a point where it might only cover one or two rooms. Of the three that I have replaced for friends, I have not found a common brand, age, etc. It just seems that after time, the signal strength decreases. I know that routers are cheap and easy to replace but I'm curious what actually causes this. I would have assumed that the components would either work or not work; we would either have a full signal or have no signal. I am not an electrical engineer and I can't find the answer online so I'm reaching out to you. Can someone explain how a transmitter can slowly go bad?

Common (incorrect, but repeated) answers from slashdot include:

• Back then your neighbors didn't have wifi, now they do. They drowning you out.
  • I don't think this is likely because replacing the access point with a new one and using the same frequencies solves the problem.
• Older devices had low transmit power. Crank that baby.
  • As mentioned by a FreeBSD wireless developer this violates regulations and can physically damage the equipment.
  • It was also mentioned that higher power in one direction is not necessarily reciprocated. This shows higher bars, but not necessarily a better connection.
• Manufacturers make cheap crap designed to wear out.
  • This one actually may be legitimate although it is overly broad. What specifically causes damage over time? Heat? Excessive power?

So can anyone provide an informed answer on this? Is there any way to fix these older access points?

Wifi systems can degrade when they can't communicate with other devices on the same frequency, even with a strong signal on the antenna.

A device may not be able to communicate if it can't correctly share the frequency with other devices. The 802.11 spec requires precise timing in the carrier sense multiple access with collision avoidance algorithm. See https://en.wikipedia.org/wiki/DCF_Interframe_Space and https://en.wikipedia.org/wiki/Distributed_coordination_function

Timing requires a clock, usually a crystal oscillator. These are calibrated for the power source. If the power source degrades or drifts, the oscillator will have more jitter. With too much jitter, the system will not be able to synchronize its transmits and receives with the rest of the devices sharing the frequency, especially at higher data rates with shorter windows.

So what's actually failing when a wifi AP degrades is likely the power supply, which then causes clock jitter, which prevents the device from sending recognizable signals. The power supply can be degrade from overheating (poor ventilation), worn out capacitors, etc.

I see no reason why it should degrade (at least for such short period of time as 2 years). I've never experienced degradation with any radio devices. I see 3 possible meaningful answers for now:

1. In fact this can be caused by new neighbour routers being on same channel. You can try to manually change channel and see if that helps.
2. Router configuration is somehow reset to lower power output (many routers have ability to set their power output thru configuration).
3. Same as 2, but premeditated by manufacturer (planned obsolescence).

I asked our sysadmin at work, he also never noticed something wrong with our 2-years old and cheap TP-Link Wi-Fi point. No noticeable signal power degradation at all (we allocate large area, so weak signal would be immediately noticed at far rooms).

Update. We recently upgraded our Wi-Fi network at work, so I had a chance to personally test an 8 years old ZyXel P-334WT EE wireless router which worked 24/7 in our office. I've not noticed any weak signal problem compared to my rather new router.

So in addition to my previous assumptions I could only think of really low quality components, that degrade their quality that fast.