The answer you found on Yahoo is mostly wrong. The basic statement (same as dpollitt's answer here) is correct — theoretically, image quality shouldn't degrade but a number of factors might make it worse. And the list of things that might go wrong is sound enough. But the mapping of symptoms to problems is very inaccurate.
Point by point:
One would be dust accumulation on the sensor which leads to resolution loss, pixels of false colors, noise, spots.
This can definitely lead to distinctive dust spots. However, for there to be overall resolution loss, there'd have to be an even coating of dust, which seems unlikely. False colors and noise are unrelated.
Worn-out moving parts can lead to the sensor moving off its original position, which can lead to out of focus images, blurry and distorted images.
Mostly true, although the relevant parts should be pretty sturdy unless you smash the camera. But distorted isn't very likely. A loss of alignment could lead to uneven focus, where half the frame is in focus but the rest isn't, as with a tilt/shift lens (except without any control).
Improper maintenance can lead to blown-out receptors on the sensor, which can lead to blank spots on the image, false-color pixels and resolution loss.
This is just wrong. Stuck ("false-color") pixels are common, and can increase as a camera ages, but they're not generally due to improper maintenance — unless you're taking long-exposure pictures of the sun, and that case the damage is likely to be distinctive. "Resolution loss" isn't an issue here: if you have a 10 megapixel camera with an insanely-high 1000 dead pixels, that's only 0.01% of the resolution!
If you camera is a compact camera (lens not interchangeable) then dust might have accumulated inside the built-in lens, which can lead to noisy, blurry and distorted images.
This is more likely to lead to the lens getting jammed than to the problems described. In general, dust in the lens is undetectable, although if it's on the rear element you might see some light shadowing under certain conditions. If it's a huge amount of dust, you'll have a small loss of resolution and contrast. (Not "noisy, blurry and distorted images".)
Also the lens coating might be scratched or gone altogether which makes your images more susceptible to distortion or false colors due to ultraviolet and infrared radiation reaching the sensor. Ultraviolet radiation is known to produce wash-out colors.
It's possible that the lens coating could be damaged, but it's very unlikely that it's gone. And it's true that unfiltered UV can be problematic, but digital cameras almost universally have a built-in UV filter right over the sensor — this is not the function of the lens coating.
A missing lens coating would make your lens more susceptible to flare and to veiling glare, which could reduce overall contrast. A partially-damaged lens coating would probably be a visible scratch, and that basically falls under the same category as dust in the lens.
So: a digital camera is a precision device, and there are parts that can go out of alignment. Extreme factors (or abuse) can make this happen. Generally, you shouldn't need to do an regular maintenance, or send the camera in, although if you have a nice camera you keep for several years a checkup now and again won't hurt — especially if you suspect a problem.
But the main reason it seems worse, I think, is the same one that makes my once-fast desktop computer now unbearably slow — expectations have changed.
