This has come into picture as Software as a Service (SaaS) and Platform as a Service (PaaS) models have evolved over a period of time. Here, the buyer need not need make upfront investment in hardware and software, rather these come as bundled service to them. Few examples where these are prevalent are - Finance & Accounting (Core Finance), Human Resources (Core HR), Analytics (Business Intelligence/Reporting), Procurement etc.
There are also scenarios where the software vendor provides subscription of a given solution (ex. Windows Azure, Salesforce.com, Siebel On Demand, Amazon Web Services etc) on a periodic (ex. monthly, annual) basis.