All of the advice from these pro's deem to be accurate to my knowledge. I'm glad your contractor had the good spirit and professionalism to correct the issue at hand. Wood floors are probably layed parallel to the joists every day coast to coast and I bet many go unnoticed. Although the true structural integrity of the floors may not be sacrificed, the consequences are beyond cosmetic. Some floors as mentioned will experience bigger gaps overtime and most certainly more noticeable expansion and contraction movement normally hidden to the clothed eye. I remember one instance years ago in Providence, Rhode Island an 8 year old home had experienced unsightly 'humps' every where the flooring ran linear to the joists. After explaining to the home owner that resurfacing was only a temporary fix to the unsightly peaks, he opted to rip up the entire area and have new flooring installed the correct way. It almost hurt to rip up such nice flooring yet was necessary to acheive the original results the homeowner wanted.