Andrew R Stewart 

I am under the impression that tensile strength is less then compressive strength for steel. So th axle will under go less dimensional change then that of the QR. How one balances this is the art of adjustment.

To the Op's initial question- Bearing "adjustment" can change for a few reasons. The above additional pre load from the QR, improper lock nut/cone counter tightening that can rotationally migrate, Out of alignment drop outs producing off axial bearing loads, contact surface wear and pitting as well as one's ability to sense bearing "feel". Andy