I deal with this frequently with sub-contractors (and firms) doing development.
It's actually very simple.
The understanding starts out as: This is a work-for-hire. All work product is property of the company.
Which eventually leads to a contract containing:
All source-code, build scripts, documentation, keys, any other materials required to use or reproduce the deliverable item are exclusive property and proprietary information of the company.
The contractor shall not release, reuse or redistribute any component of this work in any other business. This includes any custom libraries, headers or other application work-product.
This does not apply to off-the-shelf open-source tools and libraries, however such items shall be documented and approved in advance to avoid GPL contamination.
I don't see a problem here.
I expect to pay through the nose if i want exclusive rights and ownership to someone's special library, for exactly the reasons the article dictates.
Otherwise a non-exclusive source-code license that I may do with as I please is cheaper. A binary-only license might be cheaper still.
They devs have to make a living and if it wasn't cheaper/faster to use them in the first place I'd just write it myself.
Just try explaining these legal subtleties to someone who doesn't understand software.