You can understand why many observers think Google has duplicated its efforts with the two products because the company does that all the time. However, in this case, there are some significant differences in what the products do and promise.
Buzz is an aggregation tool, and a poor one at that. You have various social network sources feed into Google so it can send out updates to people following you. But it doesn't cover the range of social networking sites that a good aggregation tool would, doesn't let you post to those sites, and blurs the distinction between sites built on mutually-agreed relationships (like friending on Facebook) and opt-in following (the Twitter model). I think Buzz actually all about gathering personal data for Google's own use in behavioral marketing. (Apparently the company is already planning updates to address some early criticisms, like having contact lists available for public view.)
Wave is different. It's a collaboration tool, where the point is to have conversations, both in real-time (chat) and asynchronously (like email), and tie them into document-sharing and information processing. Wave is still marked as in a preview stage, but the potential is astonishing.
But Wave faces a problem: Google is as bad at explaining products as it is at marketing itself. A number of critics, like Robert Scoble, dismissed the product early on as even less productive than email. Wave isn't an email replacement -- it's more like collaboration tools such as Lotus Notes or Campfire. Yet that also highlights the challenge Google faces in getting users to adopt Wave: Collaboration applications are notoriously difficult to explain, and as a result, it's hard to get potential users to understand and embrace them.
There are many aspects to online collaboration: document sharing, email, chatting, telephone, shared web resources, and scheduling, to name a few. Much of this already appears in Wave, and there are already some extensions, including a yes/no/maybe facility to gauge interest, mapping, video chat, and weather conditions for given locations. Using Wave is like having a virtual room where people can drop by at the same time or leave supercharged notes that can attach themselves to specific lines of discussion.
Buzz seems like nothing more than Google emulating what Yahoo as tried to do, with neither offering anything that does what people who use social networks really want. Wave is a real attempt at innovation -- doing something different that might have value for an audience, somewhere. It's the impressive beginning of a tool suite that will let people do truly new things -- if only Google can keep them interested long enough to figure that out.
That's the challenge. My bet is that most people with access to Wave know relatively few others who have it, so they don't get to experience its utility. Given Google's lackluster communications skills, it may take a long time before people grasp the big idea.