Same situation for me, splitter plus A/B switch as described on Comcast's own website for reception of HD directly thru the wall
Connect a Standard Definition Digital Transport Adapter to an HDTV
I both did online chat and phone with 4 different agents and all tell me there has absolutely been no change in our service and that I should still be receiving HD via the splitter. Just another example of Comcast having no idea what Comcast is doing. I did however not enjoy the chat agent attempting to tell me I was stealing HD as I did not subscribe to HD service, until I sent her to Comcast's own instructions on how to do it. She did not apologize, just moved on to not help me.