Certainly, but nobody really uses the term for such services. Salesforce.com likes to call itself SaaS because it distinguishes itself from Siebel, Oracle, and other big enterprise software co's that sell similar services using the old product model.
But it doesn't really mean much outside of the enterprise space. The whole web is SaaS. =)
Software used to be something you buy for a lot of money in a physical package.
Software as a Service is sold by license for less money over a specific period of time and used over the web.