My understanding is that the salary of other types of workers do not follow this rule.
If that’s correct, then the section means software developers are actually special snowflakes treated differently by the tax code
Untrue: for example, if you are a lawyer employed to help a company acquire real-estate or another company (i.e., a merger) then your salary is treated the same way by the US tax code (i.e., your employer must amortize your salary).
If you want to argue against the current tax code, point out that currently companies do not have to amortize the pay of executives even though arguably their work fortifies the company's ability to make a profit in future years like the work of software developers does.
A recruiter, or an HR person in general, do work that “fortifies the company’s ability to make a profit in future years” as you say, by hiring people that will hopefully work there for years.
Same as a financial analyst implementing new processes and spreadsheets to better control money spending.
One can argue that most white collar worker is investing in future profit. Sales people nurturing long sales cycles, lobbyists, content marketing, SEO.
Why are software developers (and merge lawyers) snowflakes among all those types?
If a recruiter or HR worker helps a company hire 100 new employees, all 100 are free to quit at the end of the year whereas the artifacts created or improved by a developer will be the property of the company forever.
In other words, maybe it is a bad idea to treat people (employees in this case) like property even in our tax code? (I'm personally OK with software's being treated like property.)