Pricing of an xONEx rtw (and of competing products) varies quite a bit depending on the country in which the ticket is sold and where the trip begins. They invariably must be the same place to realize the saving - if you buy a ticket in the U.S. for travel beginning in Colombo, you'll pay the much-higher U.S. fare.

Arranging and pricing an rtw can take something between hours (unlikely) and a couple of weeks (also hopefully rare) so most people like to make the arrangements in advance. Since the sale must take place in the originating country (and some airlines are reportedly grumpy even about making the booking from the U.S.) having an agent in the originating country is considered indispensible by many here, but if you're the gambling type you can show up and try to make the arrangements there, with the airline ticket counter.

In many cases the airline is willing to be the agent, if they have an office there. About the only advantage of using a travel agent is that a few are willing to FedEx paper tickets so you have them in hand and have one less thing to worry about.