It's not so much that you can't fly from VOR to VOR, everyone knows how to do so. It's more that it's a horrible waste of time and fuel.

If you have GPS, you will get cleared direct after getting out of congested areas, usually (presuming you are capable of clearing all of the terrain between point A and point B). If you're having to fly from VOR to VOR you will fly a much more indirect route and spend a lot more time and fuel, particularly on private jets.

Hence the offer to put private jets on vectors rather than tell them to fly the old fashioned way. People on private jets tend to be people who make political contributions, who in turn tend to call the congressmen in their pocket and complain.