I personally find the price for in-flight WiFi to be an excellent deal, considering the technological feats required to make it happen. You're communicating over hundreds of miles from a metal tube going 600MPH. Often you're talking to space! And you get to use this for, what, ten bucks?
I don't always pay for it, but it's a great deal when I need it.
Currently, in-flight Wi-Fi hums along at 3 to 10 Mbps. For the whole cabin. Pricing it at zero would slow it to a crawl. This is true for any rival good.
200meg @ 5 GBP sounds more reasonable...enough to surf a decent bit but not enough to affect overall speed.
They do, of course, restrict video streaming services so as to not let one person consume the whole downlink, but that seems like a reasonable tradeoff given the bandwidth limitations on satellite internet. Many airlines now have onboard video-on-demand services anyways, which fills the streaming niche for most people.