Categories like this are typically defined by the analyst firms, such as Gartner and Forrester. Most often, the analysts base these definitions on existing products. This makes good sense, since the goal of a category is to provide a way to think about the area and to compare different offerings. For BPM, this definition has largely been driven by small firms, the companies that are sometimes called "pure-play" BPM vendors. As big companies adopt the BPM terminology, however, the definition of this category is changing.
For example, Microsoft provides everything on the list above, but not in the same way as the smaller BPM firms. Rather than supporting human and system workflow in a single engine, for instance, Microsoft splits them in two: human workflow is provided by Windows SharePoint Services (and Microsoft Office SharePoint Server), while system workflow is supported by BizTalk Server. Similarly, a good number of people would argue that to qualify as BPM, the tools used to define workflows must be usable by business people, not just developers. Once again, Microsoft's view is different, as its tools are targeted more toward technical people.
Given these differences, it's possible to argue that Microsoft doesn't qualify as a vendor of BPM technologies. Yet this is a difficult position to support for a couple of reasons. First, most of Microsoft's customers probably will see it as providing BPM, whatever the analysts think. I've put this question to hundreds of them in my recent talks, and a large majority (although not all) believe that what Microsoft offers certainly is BPM. The second reason to view Microsoft as part of the BPM world stems from the point mentioned earlier: in new categories, the original definition is commonly driven by small firms, then changes as major vendors enter. A great example of this was the application server category, which wound up looking almost nothing like the original products that carried this label. Arguing that Microsoft's products don't qualify as BPM because they don't exactly match the original definition seems as odd as claiming that WebSphere Application Server doesn't deserve to be called an application server because it's so unlike the Kiva or NetDynamics products that originally gave this category its name.
As new products appear, especially from major vendors, they change the definition of a category. Expect to see this happen once again with the definition of BPM technologies. And whatever analyst firms might say, expect to see Microsoft perceived by most of its customers as part of the BPM world.