I can think of few reasons, why the term should be longer than the lifetime of the author, but I don't think it should be any shorter than that. The current situation of life + 70 years is ridiculous.
I was invited to sign up for Blogburst about ten days or so ago, and wasn't frantically impressed when I checked them out, expecially after discussing it with some people and reading your article. This service looks more interesting and worth considering.