One thing I'd like to point out (again) is that following MM as a non-Japanese speaker, and following them from the native perspective is like following two different groups. Those of us who can't follow the radio shows, and the concert banter, blogs etc., or who struggle in terms of fluency, are missing out on a lot with respect to their personalities. Even if you're 75% fluent, it's that last 25% that contains the most subtle humor and most sophisticated content.
As a result, instead of looking at the girl's entire image, as foreigners we tend to focus on the physical traits of the girl. Or the broadest most-slapstick and least refined forms of humor. So, if a girl gains weight, it stands out for us because her appearance is such a major aspect of how we think about her. Or if she's less goofy than before, it comes off as boring because who she's turning into needs more than pantomime and Nihongo 101 to appreciate.
Yes I AM overgeneralizing, but I think at least some of the overemphasis on physical traits has to do with this.