In the following article we can read an argument of Software Assurance as an extortion tool to get more revenue for Microsoft:
However I think the article misses the opportunity to also explain the other side of the coin. Software Assurance (SA) not only includes new editions release over the term of the coverage, but as well benefits like the ones listed below these lines.
An honest and accurate calculation taking in consideration an organization desired upgrade cycle, shows that within 5 years more or less the investment of Software Assurance offers savings compared to buying the software again.
The article refers to Enterprise CAL as an example of a sku that must include SA. It is important to mention that one of the benefits related to the Enterprise CAL is actually the availability of funds, called Packaged Services, for Assessments that a Microsoft certified partner can use.
Possibly Microsoft can do a better job at clarifying road map of releases to clients and marketing better SA on their renewals. However the article in my opinion misses a true comparison of the benefits and costs of SA to help readers on the development of their own impressions.
Last, Google is a real competitor, I agree with that, however the arguments of security, training for users and other aspects of the IT policies in organizations is worth discussing as price is not all when IT is essential for productivity.
Full list of SA Benefits: