From the minutes of the 20th FRA General Meeting:

Phase out of 40Mhz - A number of safety issue with 40Mhz were raised, due to the increasing number of robots in certain melee fights due to the use of 2.4Ghz controllers there have been a number of issues where robots on 40Mhz have been out of control/ uncontrollable due their signal being drowned out by the large number of higher frequency controllers. Proposal was put forward that as from Jan 2010 all featherweight or larger robots should use either 459Mhz or 2.4Ghz
Decision - Agreed (Unanimous)
Was it mentioned before the meeting at all that this issue would be up for consideration? Don't recall seeing it anywhere, as I would've stated my disapproval of such a move had it been up for discussion on the forum. Would it not be better to have it come down to the discretion of the EO as to whether they would allow people to operate on 40MHz, as its their own arena marshall that's responsible for the arming/disarming of potential out-of-control robots? (a risk that should be reduced if the robot is fitted with a working failsafe - which would be, let me think, every robot!)

I guess it could be viewed in a similar light to the current discussions regarding the power tool drag racing; I paid £120 for my Skysport 6 when I bought it new and it still works perfectly fine. I could do without having to fork out a further £60 (minimum) for a DX5 and RX (£120 if I want to run two robots) and I'm sure new builders who are operating on 40MHz could do without that added cost too. Yes I have decided that I will go to the effort of building a drag-racer to enter the Robo Challenge event, but that's a one-off entry requirement. This rule would affect every event from 2010 onwards.