In a podcast on IBM developerWorks, Dave Michell explains about Software as a Service (Saas):

the customer does not take ownership of the software, but they're going to rent this solution in a subscription model, and it's delivered remotely. And that's very different from the ASP model. In the ASP model, or the application hosting model, what the customer is doing is they're buying the software.
[...]

In the Software as a Service model, again, the customer does not own the software. They subscribe to an offering and they buy that offering in a subscription model per user per month. So there's no software purchase to be made.

And the other key point here is in the Software as a Service model, the customer really has no say over what the infrastructure is. They don't get to decide what the hardware is or the middleware or the database — and more to the point, they don't really care.

So in the SaaS model, the customer says "I want to buy that application functionality. I'm willing to pay this much per user per month," usually is their typical model. "And the service-level agreement meets my needs. So I'm going to acquire that application that way."

Considering a configuration management system, such as ClearCase, many customers struggle with configuring the system for optimal performance, setting up and configuring servers, network and client parameters. In many cases, the users don't really care whether it is ClearCase, Synergy or Subversion behind the scenes, as long as that can do version control, baselining (or labeling or tagging), parallel development (or branching or streaming), delivery, rebasing, releasing, status promotion, structuring, setting attributes, and all the other CM stuff. Users don't care about sufficient licenses, disk space, replication across sites and other IT issues; they just want the system to be available and to work properly to their needs.

So, the CM system seems a perfect candidate to be deployed as Software as a Service. Even more, if the CM service is offered as a Web 2.0 application, the internet will be the platform allowing local and global accessibility.

If in addition there would be a standard set of CM service features, the CM back-end could be supported by just any CM vendor that complies with this standard. The front-end could even be of a different vendor or proprietary to the customer, e.g. as a dedicated integration with other systems. Customers could then focus more on the tool-vendor that suites best with their organizational and IT needs, and users could better focus on dealing with true configuration management issues, rather than being hampered by infrastructure and IT issues.

Why wouldn't a product like ClearCase be offered an SaaS model, if IBM is such a promotor of SaaS?