Somewhere along the way, the idea of "grassroots" (i.e., citizens communicating with elected officials) became synonymous with "mass e-mails." Conversely, "grasstops" became synonymous with personalized communications.
I'm not sure why or how that happened. In my opinion, "grasstops" communicators are those that have some sort of relationship with an elected official or are opinion leaders in the community. "Grassroots" are people who are connected to an elected official's office through constituency and are generally more "rank and file" citizens.
But that doesn't mean that "grassroots" citizens should be consigned exclusively to mass e-mail campaigns -- they can develop personalized, thoughtful messages as well as anyone else. In fact, they SHOULD develop personal messages because, well, they work!
Check out this interesting article from Politico.com on grassroots / grasstops (grass middles?) techniques.