I am almost a 100% sure that what Paul says is right. I think WGT brought it out in this one format to test it. I have read about someof bugs, people getting blue screens of death and having to forfeit and other such issues
It would suck to setup a really nice CC bracket and part way through people can't finish their rounds or if the brackets had credits tied to it and someone paid a 100 or more credits to enter only to lose them because of a glitch in the system.
WGTIcon has already asked in numerous threads for people to submit bug reports when stuff happens in the brackets, so they can look at them and address them. So, I think it is probably their intention to do brackets for credits in both tiered and open format. Hopefully they give it to the CC, but ya never know!