Different Web Service Providers
If you look at the markets for ISPs and EDI, you'll find that different types of services are being provided. It is likely that similar roles will also evolve to support Web services:
Tool vendors, whose companies offer tools that enable the other parties to work. For example, HTML editors provide tools that help Web site developers in their businesses. With EDI, the tool vendors offer so-called "EDI translators."
With Web services, the vendors are different and their products are more sophisticated (application servers), but the need to offer products remains.
Developers, in the broadest sense of the term. These are the companies (and sometimes individuals) that build the Web sites or design the EDI interface. They may be part of the IT division or they may be subcontractors.
Similarly, you should expect a lively development industry will develop for Web services.
Host providers and Value-Added Networks (VANs). (The latter is popular in the EDI industry.) They are responsible for running and maintaining the Web site or the EDI network.
Given the complexity of Web services, you should expect that companies will specialize in offering those services.
Note that hosting comes in different sizes and flavors, from hosts that serve the largest publishers (for example, Akamai, http://www.akamai.com) to hosts that serve the SoHo markets (for example, Pair Networks, http://www.pair.com). (SoHo stands for Small Office/Home Office businesses.)
Web Services for Smaller Businesses
I cannot stress enough the importance of providing services for small businesses. So far, the Web service industry has concentrated on the largest players. For example, application servers cost several thousands of dollarsway out of reach to the smallest organizations.
Yet the Web has grown in popularity because it was accessible to every company, no matter its size. For Web services to develop, they will have to be similarly accessible.
Again, it is interesting to compare this with the evolution of EDI. EDI started as a solution for large organizations: Banks, car manufacturers, and utilities were among the early adopters. Only those companies could afford to build and run an EDI system. However, one of the things they learned quickly is that to do commerce you need at least two parties: the buyer and the supplier. Likewise, to do commerce electronically, you need at least two parties that can interact electronically. The technology has to support this and, frankly, EDI has never been very successful in that respect.
It is interesting to notice that this lack of success with small enterprises happens despite the fact that a large subsegment of the EDI industry focuses on enabling the smallest organizations to participate in the process. (However, its primary motive is to find partners for the largest corporations.)
A capability to reach out to the broadest base of partners, and therefore to provide affordable services, has been a key differentiating factor between various EDI providers. It has also been a key element in the success or failure of EDI projects.
There are no reasons to believe things will be different with Web services. If you are looking for a profitable segment in which to specialize, you might consider enabling Web services for the small and medium-sized organizations.