I would really hate to train in a dojo that made that an actual rule and where sempais felt they were justified in 'correcting' me for not giving them enough 'respect'.
Real respect is _earned_. If someone keeps giving good advice, I will quickly learn to listen to their advice - and it won't be because I was told they're my senior so I have to.
Not sure but think you may have misunderstood the point. The respect should be there for your sempai from the get go. That way you don't get into a pickle, like 5th kyu's handing out advice to 2nd kyu's. This etiquette is inherent in the Japanese social hierarchical system. And although we are not Japanese nor are we attempting to become, it does lend itself to creating a well ordered and structured learning environment. Which is for the betterment of all deshi.
A sempai will not correct a student for not showing them respect, they don't have to, the instructor has taken care to ensure that everybody understands the correct etiquette from the get go.