All software is a commodity

I Agree; this is often what happens to companies that don't have an executive team with tech knowledge or don't like hiring "Disrupting" people (Banks, Government, Law firms. Largely in "Old Business" sectors).

They often have an IT department that will buy anything that require more hires to maintain and makes them more relevant in the company.

"If you job depends on not knowing something..."

A great example of this type of enterprise software that locks you in proprietary hell is "MS SharePoint".

I disagree. In the fields that I have worked in ( games, finance and advertising ), although a lot of open source software is used, mostly in the form of libraries, the final product is highly customised and can not be replaced with bits and pieces glued together.