What you do need to factor in is that if you are doing an RTW that takes a while your plans might change.... Then the change fee is a relative small price to pay to change your remaining flights or even do a complete reroute. That's something most other offers or promotions won't have.

And I don't really understand your point about any side trips, 16 flight segments and the ability to have 3-5 legs in a single region make most routes possible.