I kept my Comcast high-speed internet (need that for Netflix and Roku) and can tell you I can receive absolutely ZERO HD channels via Comcast on any of my SmartTV's. Nothing. All the channels here have been moved up to a Digital tier which require their box to receive them. No two ways around that.
IN HD:
ABC
NBC
CBS
PBS
Fox
WETA
IN SD:
Bounce
Ion
The CW
Country
This
WGN
CSPAN
CSPAN2
Weta kids
Weta UK
As well as some local channels from nearby cities. Maybe its just the way its routed around here, but I learned about it from a friend at work who learned from a relative in another area and it works for all of us. Good luck.