Web services minus 'wetware' equals difficulties.
The Hewlett-Packard calculator marketing site shown here is obviously "soft" to the point of being downright squishy, as witness the error message thats seamlessly interleaved with its dynamically generated content. Web services developers would do well to think about the failure modes that their sites, or the services sites on which they in turn may depend, might incur and the manner in which those failures will appear to service consumers.
Its one thing when a "Web appliance" is a thin device bearing a Web browser, with a highly adaptive, post-processor stage in the form of a human viewer. Its another thing when a Web appliance is a "headless" device, with no user interface at all, but only embedded software interacting with other devices and servicesand with no imagination or ability to distinguish between exceptional data and extraneous noise.
Without the included-at-no-extra-cost assistance of a live users "wetware," Web services development is going to be a much more difficult task than traditional Web site design.