Since I tend to travel independently, on much less money than I used to(!), I search and book for exactly what I want. I know that, sometimes, this will cost me more than if I used an agent or travel web site [insert any of the many names here!] but I would not be able to get the travel agent to search to very low levels of detail that I sometimes want. Simple example, I might choose which flight on a particular day by the type of aircraft operating the route and so on. If you ask them for too much detail, too often, then they have to charge you more.
For some folks, they have the money but not the time to search and book their own trips. There will always be such and there will always be agents to handle them. However, I expect that they will increasingly be small companies or folks working form home to do the research - not the big plate glass shop in the High Street or shopping mall.