Burning a CD part II

I recently posted regarding issues with problems I was having with Burning of CD�s. I thought I would share this with all of you as it just goes to show how really weird this interest of ours can get. I followed the suggestions made in response to my first post going to a better brand of CD and burning several copies at 2X instead of 8X. And ., the problem persisted. So I tried one of the problem CD�s on a portable player I have as my daughter commented on not having the same problem when she burned a copy and played it on her own system, and every copy I tried played perfectly. At this point I suspected my CD player. Off came the cover, in went a CD, press play. Here is where it gets weird. The CD was spinning eccentric when I hit play(in this case it was a copy I was playing),I got the jittering effect (not to be confused with the technical term) I tried to describe in my last post, as if the Laser were having a problem tracking the recording, sort of a crackling/jittery sound. So I put in a commercial CD, same wobble, but it played perfectly. All of my commercial copies played normally, many, but not all of the burned copies had a problem.
To make a long story short, I moved the upper capture hub out of alignment, to see if the lower drive hub would pull it back into alignment when it engaged the disc when play was pressed. Sure enough I pressed played, and the upper hub snapped back into alignment and was now turning the CD concentrically. In went the same CD�s that were not playing well, and all are now playing well.
I have two questions:
1) Is it possible for this assembly to go out of alignment from a physical shock for instance or could this be indicative of something wearing out?
2) What is the deal with all of my commercial CD�s playing just fine while wobbling and a high percentage of the Burned CD�s not being able to?