As someone who previously used to do an award service as well as other similar flight searching kind of services, let me just say that it's not any specific "special" expertise that you're paying for - not to say that the huge learning curve of being an award expert like Ben or his colleagues is an easy feat, but it is more the time and energy required (or grunt work, if you will) involved in actually piecing together these itineraries, then booking them (sometimes manually by phone) that you're paying for. In some extreme cases, $300 is a very small price to pay for the luxury of pawning of all the workload to a third party.
Of course there are also much simpler award tickets bookable directly online - for these, the time savings and hence value generated by these services I would agree is a lot less. As with all these things, YMMV.