It's not true. People who have an existing ticket are not being asked to pay for the difference to the new fee.
There was a poorly worded email that went out to some people and created confusion. That email was pulled. VX never planned to ask existing ticket holders to pay the fee difference.
Has VX considered having "unofficial" representatives on these forums, who do the usual "while I'm a Virgin America employee, I don't speak for the company in an official capacity" disclaimer? I notice the AS forum has a number of these people (and they are uniformly pretty awesome), and I think it would help with things like the dark 319/poorly written emails, and I think it would help for VX as well.
And yeah, that's really bad if that email was that badly written. I'd go pretty ballistic if I paid IN FULL for something and got told "we changed our prices and now you have to pay more".