The simpler the Saas service, and the lower cost of switching, the more competition and commoditization that may go on. But this article is talking specifically about Saas replacing enterprise software. Software is sticky, and some software is very sticky because it is mission critical, highly integrated into the business workflows, and/or there is significant user interaction.
For example, if a company has 500 sales people all happily using salesforce.com, why would a CIO disrupt everyone's work to switch to a cheaper but different product? The cost of salesforce.com is not a significant cost to the business, but the cost of disrupting people's productivity swamps any savings you might from switching to a cheaper service.
This is similar to someone telling a company to drop MS Office because OpenOffice or GoogleDocs have equivalent "good enough" functionality and are free. There is no 'commodity' version of MS Office which looks and behaves exactly like MS Office but just with a lower price.