I have a little (actually a big) problem concerning usb ports.
In the past I had a laptop, and after a few years, the USB ports would drop out on me one after another.
First, the usb device (for example a mouse) would work only when you laid the cord in a certain position. But after a while, nothing would work on that port anymore. => I ended up with no working USB ports and had to replace the laptop.
I suspect it has something to do with the inserting and pulling out of devices numerous times, which damages the ports?
I am really carefull now each time I insert my mouse, and don't try to stress the ports by wrong movements.
But 10 months ago I bought a Macbook Pro, and for about a month, both USB ports are not barely functioning! (1 has died, the other one only recognizes the mouse when I lay the cord in exact positions)
It could be a variety of things. Like you said, it could be damage due to being bumped around a lot or it could be that because it is on your lap constantly, it isn't cooling as necessary, which in turn could damage the usb controllers on the motherboard. Like I said though, it could be a variety of things.