If buzz were a good product it would stand on its own merit without needing to "leverage" gmail. The trouble is that it's not a good product -- it's a lame me-too effort that offers little over its rivals (Twitter and Facebook). Me-too is fine so long as you bring something to the table, and buzz doesn't seem to, except for gmail integration, which an awful lot of people think is actually a hindrance.
Google have shown time and time again that they don't get "social networking", which is fine because they're a search and ads company and they do get those[1]. (I'm thinking of Orkut, OpenSocial, the way they introduced following into Reader and now buzz).
[1] the recent facebook login debacle aside