WGT should implement this, though: purchasing credits for another WGT user. This is extensively used by last.fm, for example. See their FAQ – Subscriptions, question "Can I purchase a subscription for another user?"
It doesn't seem like a good business strategy for WGT to be voluntarily diminishing their revenues. Doesn't WGT need every dollar they can get, so that they can faster develop the features that everyone has been clamouring for, like variable pin placements & new stroke-play courses?
So, it's probably not smart to reject money from people who'd like to pay it, in the form of buying credits for fellow WGT users.
(Compare the "Masters-only" clubs situation; the introduction of these clubs likewise meant WGT voluntarily chose to lower their potential revenues from equipment sales. 
Wouldn't it have been economically more feasible, for example, to sell the Master clubs to everyone, but with a 100% surcharge for non-Master players?)