Understand that the weight thing is a non-issue for probably 99.9% of bike purchases. Even relatively dedicated riders that are buying a good bike for fun and/or commuting aren't going to care. Only the racers (including tri-athletes) and time trials riders care about that level of minutiae.
My first disc brake equipped bike (recumbent), I bought because I had just moved to Seattle and wanted better wet weather performance. That alone was huge to me, and it was quite noticeable. I had good 'wet' rim brakes, but their performance never came close to the performance of discs. My bikes are 99% used for commuting. By the time I put a rack, lights, panniers, etc., the extra weight is a non-issue.