I have often wondered at linearity problems.  E.g., why is the BMI formula based on weight divided by a <i>square</i> of height when geometry says that weight is proportional to the <i>cube</i> of (similarly proportioned) height?  Probably, in the region of interest, the one curve approximates the other, but why fight locally Euclidean fidelity?  Feedback mechanisms are common; unless you look for the correct function (whether polynomial, exponential, factorial, etc.), as implied by the <i>underlying mechanism</i>, throwing regression at the problem is going to obfuscate.