My mother lost 60 pounds three years ago. She got tons of comments on her weight and how good she looked (she happened to be embarrassed by it, but that's another story). There were three people in the community, though, who pointedly did NOT comment on my mother's weight loss. The thing that these three people had in common was that they had tried all sorts of diets and methods of losing weight, but failed every time. They were mortified and jealous of my mother's weight loss. So, some people who don't comment are just plain thinking of themselves, and how they wish they could do what you've succeeded at.

The rest of the people who don't comment probably don't want to hint at the fact that you used to look larger than you do now. Chances are, though, that once you lose more weight - once it's glaringly obvious that you're, say, four sizes smaller, people will be more open about it.