Hmmm, well, I suppose they have a point, but the movie can probably be compared to others as well. I personally don't get the "Gone with the Wind" comparison, but I'm sure it meant a lot to whoever said it. I'm interested in knowing why they might think that or why you did, brokeplex.
For me, the first comparison that comes to mind is "A Street Car Named Desire" with Brando weeping over Stella. It was a groundbreaking film that changed the way everyone acted thereafter. No man had ever appeared so strong and so weak in one character, so vulnerable and sensitive, but also tough. These qualities are in Jack and Ennis too and Brokeback Mountain was a groundbreaking film to me. It was the first time I ever saw a truly serious love story about men... They weren't "queer" in outward appearance or manner, they were just men in love like so many in the past who have hidden it, but the film hid nothing! It was not only daring but it's was an "our time has come" event. Those are my thoughts on it.
Now, I was in a store recently and had "Roots" in my hand, the entire story, but didn't get it. I think I will now, because I never saw it. So, I'll have to get back to you on that later.