Have you ever wondered how someone who has never been to a place can figure out how long they will want to stay there? I go, I stay, I leave when I am ready to leave and not before. Seems to work out to exactly the right number of days in a place every time. ;-)
Like all things, it's circumstantial. If people don't have to be in a certain place at a certain time, then of course that can be a great approach. But not everyone can have that unstructured a life. I know, for example, that you have very strong feelings about RTW tickets and the "structure" they impart to travel. But the majority of alliance-based RTW tickets are actually sold to people who use them for business, who have appointments, deadlines, and other "structures" imposed on them.
One night I was on a flight from Vancouver to London (was the last person to board because of a hideous mis-connect, but that's another story) and while I was catching my breath and thanking the travel gods, I chatted with the fellow sitting opposite to me (in a BA business class "pod" facing forward, while I faced aft.) He was on a trip to visit his company's offices in London, to be followed by visits to offices in Mumbai, Hong Kong and New York, before returning to his home base in Vancouver two weeks later. He does the same trip (with minor variations) six times a year, using RTW tickets in the process. Doing so saves his company something like $50,000 a year in his travel costs alone.
Certainly a different sort of travel than the kinds talked about on this forum, but maybe a little illustrative. Not all travelers can pursue open-ended itineraries or sing Val-de-ri nonstop.

