I think if push came to shove YIHI would be forced to honor the warranties for those who paid less than retail. Price fixing is illegal in the US. If the situation was brought to the BBB I think YIHI would have to abandon their policy.
Sure, maybe, but that's a hassle the end user shouldn't have. It's not a deal-breaker in itself, obviously, but one more strike against Yihi, imo.