Does ATSC QAM mean it has a built in HD tuner ?

I think so....and cable non-scrambled hi-def. My computer card picks up Comcast non-scrambled hi-def QAM channels, and I think it would do the same thing for over the air, if I hooked an over the air antenna to it.

I'm no expert though.

Dave

Yes, it will pick up HD OTA
QAM (quadrature amplitude modulation) is capability to tune from those digital cable feeding
(cut&paste)
A QAM tuner is a electronic tuning device. The qam tuner is used in digital television sets and other electronic equipment, such as vcrs and dvrs. QAM stands for "quadrature amplitude modulation". Qam is the format by which digital cable channels are encoded and transmitted by the cable companies. A qam tuner can tune non-encrypted, digital cable channels, without using a cable box (set top box). If your set has a built in qam tuner, you can simply plug the cable from the cable company, directly into your TV set. This will allow you to watch non-encrypted programming. (Encryption is used for programs such as HBO and Showtime).
Regards
Thuan

Over-the-air and cable HD transmissions use different modulation schemes. ATSC (Advanced Television Systems Committee) is the standard for over-the-air transmissions and uses a 8 VSB (vestigial sideband) modulation scheme. As someone else pointed out, cable systems use QAM (quadrature amplitude modulation).

Bottom line is that the set you saw in the ad can receive both over-the-air HD transmissions and unencrypted cable HD transmissions.