eBay claims 5.7 billion web service calls a month! I wouldn’t be surprised that in the future, the number of total web service calls to be more than the number of manual page views.
While people visit the web and create the web traffic to mostly view content (including email which is a major contributor), using web services people can create creative and innovative applications that can be either online or on the desktop and provide facility to view and also create content. People making serious living out of eBay for example with hundreds or even thousands of listings would rather create their lists through a specialized tool that makes use of these web services than to do it online.
eBay has Shopping Web Services and Trading Web Services. They also have Research Web Services but I don’t see an XSD for this yet.