Well I'd argue that's not quite true either. I checked Hallmark's programming into the near future and it looks like this is a "Christmas-in-July" thing. There are Christmas movies in August, but they're more sparsely spread out throughout the week.
Unfortunately, I'm really speaking from experience. My grandmother watches it all day, so I vaguely know what kind of programming they have.
Also, even if there was a fully Christmas channel, its existence wouldn't really be indicative that the majority of Americans are Christmas-obsessed, just enough to have a cable TV channel. There's also a science fiction channel, but I wouldn't use its existence to argue anything more than that there exist enough people with enough interest to warrant a sci-fi channel.
I guess my point is... I'm inclined to agree that it's strange that many Americans are so interested in Christmas. I'm also inclined to agree that Americans are obsessed with religion and ramming "traditional" values down everyone's throats. But I disagree that your image is necessarily an indicator of that obsessiveness. The plethora of Evangelical Christian channels would probably be a better example.
I work with hospice patients, and Hallmark is one of the more popular channels I see on in homes (the others being Game Show network, Food Network, anything showing old sitcoms, and Fox News.) I've even known some families to use their Christmas in July programming to let Grandma/pa think they made it to one more Christmas so that maybe they'd let go.