Coupling between RF devices and other electronics is a real threat. If electronics aren't properly shielded they are susceptible to stray RF. I think the CAA took this cautious stance due to the relatively old fleets our domestic carriers are operating (Kulula ~ 25 years, BA (Comair) ~ 22 years). These planes weren't designed to cope with modern RF devices onboard and the flight systems can be influenced by them.
Modern planes are designed with these external elements taken into account - which is visible on flights in Europe and the USA where onboard use of mobile devices are allowed. So, I assume the WirelessG service won't actually be available on ALL flights, just the more modern planes...
It would be awesome to have some sort of connectivity at 10km - Sudoko gets boring after a few hours and SAA's IFE is not quite up there
It does not make sense what you said. If RF was so dangerous for older planes then they'd ban all communication devices - or at least confiscate them to make sure they were off. As is, they have no way of knowing if you've really switched off your phone, purposefully or not. Your laptop or netbook also has a Wifi/BT/3G transmitter. Also you may forget your active phone in your luggage. If these things were really dangerous, they'd do more to ensure that these ubiquitous devices were switched off.