Shameless plug:
AirTran and Virgin have wifi available on every flight, but Delta does not. So, find out which flights to book on Delta @ http://www.haswifi.com
The economics of in-flight wifi assume that no more than a handfull of passengers are using the system, otherwise connectivity just gets jammed. By charging, you create the scarcity that makes such a system viable.
By offering it free, you potentially make it available to no-one as suddenly everyone who has a laptop (prob most people flying in/out of SFO for example) is going to want to get on.
If I was taking a cross-country flight this holiday, I'd rather the system stayed for $$ so that I knew that I had a chance to get access to a usable system rather than turn up for my flight expecting connectivity and end up bored and disappointed because I can't get any bandwidth.
It's not normally free so an authentication page is usually required, but for this I'd imagine that Google would like to get their name in there for people who take advantage.
