Although Comcast may not yet have a "wireless" box, you CAN stream Comcast TV wirelessy through a Roku.
Here's the info.
XFINITY Stream Beta App on Roku FAQs
Although I do have a Comcast set top box, it's unplugged and in a drawer.
I have no direct cable TV connection from the outside world to my HDTV, but I stream wirelessy using the app mentioned in the link. And it's free to do this. Certainly worth a try.