Richard I don't fully understand your point, CGt delivers an amazing sales platform that is dirt cheap. No hosting costs and great means to display work and sell within a nice format on a platform that has good reputation, delivering expert marketing division and tools, providing great means to make your assets rank high and so on (large amounts of good stuff for almost noting).
I see no reason why anyone would need to bypass this?
You can have and sell on your own website but you will never have the amount of traffic CGt gets, on top you need to pay for extra hosting space and you will have greater security risks.
Besides, people who do want to bypass can do so very easily already.
Like Pumper kind of points out, noting here stops you from leading traffic directly to whatever selling point you have setup. These day's you can sell things directly on facebook, a blog, personal
website, or whatever.
However, I think it's better to invest in community and gathering forces.
We want to have al mutual beneficial parties gathered as close as possible don't we?
So if we would make use of the contact info to add them to LinkedIn or facebook pages containing a link back to the personal CGt page, then that would make the network more tightly (that's how CGt would benefit and eventually we all).
ps. one of the reason (I can think of) for having a own website is when you want to create a nice label and attach specific content (including selections of others ),and deliver your own specific presentation and browsing experience and so on.
That's also the reason I would like to host a own website, but the added cost and maintenance + security issues (also don't forget the challenge of generating the traffic) tilt advantage to CGt.
For this reason I posted a site proposal (a while ago) for a system that would make it possible to have more tools/options to customize the personal page, things like options to ad own menu and label + ability's to add work of others to the own collection (this adding would need to work like invitations maybe?)
If not, then maybe a sort of embedding tool so that the products can be embedded on a personal website (not just a link but a seamless tool pulling in the presentation content and shopping cart).