Future.Travel is a 'live' site. That means Future.Travel pulls real time data, for flights, hotel rooms, and transport connections. Your returned search is the actual availaibility at that moment. Other sites rely on 'scrapping' a live site to get the data they supply for airline flights and accomodation bookings. In order to have a quick responese they cache, or save, from previous searches and recyle the information to you. It may be up to 3 days old.... and the seats are long gone. They still have you go through the process of booking, only to tell you the price has gone up, or the seat/room is not available. Or, it may be offered at a much higher cost than what was displayed.
If you don't see an airfare or airline on the Future.Travel website there is a good chance the seats are not available, or they are at a cost that does not fits Future.Travel's 'low cost shopping' rules. You may force the search to include your 'missing' flights by specifing the airline and time / date of departure in your search request.
In some cases Future.Travel just don't provide service on particular airlines. In some cases this is because they have chosen to exclude Future.Travel from selling for them, and in other cases Future.Travel do not have access to their market (eg. we are not based in Africa or Canada - so have limited access to carriers in those areas) for supply of the ticket stock required to sell the airlines tickets.