I don't necessarily find this situation (escalating change fees) unique to Virgin, however, the strict no-change policy on web bookings seems a bit out of place. Most air carriers in the states have a 24 hour policy, which has saved me when I found I booked the wrong weekend 2 hours later. One call to Delta, and *bing*, the change was made with NO FEES.
If you pursue with Virgin, I'd stress the different set of rules that they have for phone v. web bookings. Seems like they want people to book on the web because its more convenient for them, but if you do things the way they don't want you to do, they actually provide you with more flexibility. They do seem to have it reversed.
...and if that makes no sense, I'll plead "no caffiene"