Krom--hi. For me I find all the legal aspects of their separation and divorce and the financial arrangements they've made for the children to be of interest.
Also I find the contracts issues of Jon's trying to get out of an exclusive contract with TLC and not wanting the kids to be on a reality tv show etc to be of interest since Contracts has always been my major interest in terms of the law.
I can't speak for others here--but I find how people handle these complex situations--including the emotional aspects--to be fascinating.
In terms of the general interest in Jon/Kate I think that a lot of people have an emotional investment in the children since they pretty much watched the kids grow from tiny babies--and so many people have a geniune and deep interest in the welfare of the children.
All of the above IMO only of course.