This may be the case, but I am still skeptical. They pulled support for the 622 at the last minute; it was still showing on the website on the day the Sling Adapter was released! So, this last-minute desupport of the 622 argues against your scenario, because they have known about the chipsets in these receivers forever. I think it was a long-term problem, such as marginal power supply in the 622, or thin PC traces going to the USB ports.
I actually chalk that up to a mistake by the person writing the copy for the web site rather than them "desupporting" something.