Steven,
I am really surprised that you are having such a hard time understanding this issue.
First, keeping it "simple and on topic"...
1. Are any USBC rules being broken? NO
2. Could someone file a complaint? YES - for anything, at any time
3. Could they prove cheating? NO
Now, for the more nuanced discussion that you seem to not understand...
First, my last post answered a question posed by spmcgivern...is a bowler's average independent of their ability? (You can reread my response to that question.) Simply put, YES.
You seem to think that by using a plastic/urethane ball (based on the OP), which may in fact lead to lower scoring potential, the bowler is performing to less than their ability. I call BS. It is most likely true that the bowler's scoring potential decreases, however his overall ability does not.
The USBC rule book speaks only of the bowler performing to the best of his ability, NOT to the highest scoring ability. This may seem counterintuitive, but it is not.
I think we could all agree that in most league situations (which typically involve the THS) a reactive ball will most likely lead to the highest potential for high scores. So does this imply that any bowler not using a reactive ball is knowingly performing at less than their ability? Certainly not, although their potential for higher scores is most likely considerably lower than those that are using a reactive ball. What about the bowler who has the reactive ball but, quite frankly, is too stupid to know the proper area of the lane to play and, consequently, struggles to "score" as well as he should? Is he cheating or just stupid?
The problem is the perception of intent. You believe, based on the OP, that the bowler would be cheating because he could be scoring higher. While it may be true that he could score higher, there is no way you could accuse him of cheating...unless he purposely flagged spares or intentionally picked off the corners on his 1st shot.
Walk into almost any league in this country and you will find bowlers that are still using decades-old equipment. I would guess that in 95% of those bowlers, if someone gave them current equipment their scores would go up. Does this mean they are cheating? Of course not.
And that my friend is the point. USBC cannot legislate that all bowlers should use ANY type of equipment that would allow them to score higher than they otherwise would with their current equipment. Yet that it exactly what you are arguing here. Just because a bowler has equipment that could allow him to score higher, you assume he MUST use it.
You can take issue with it if you like, but no rule breaking is occurring. What you seem to desire is this...every bowler should be trying to score as high as possible at all times and USBC should ensure this is happening. But if that were the case, then shouldn't the type of ball be mandated by USBC (the one that would be most conducive to scoring in that particular environment)? And shouldn't they provide a graph showing exactly where each style of bowler should be playing (in order to make sure that the bowler is going to score as high as possible)? Then any bowler that deviated from these guidelines would be knowingly cheating because they were NOT using the guidelines that would allow them to score the highest.
Such a thought is ludicrous, yet that is exactly what you are suggesting.