In many ways, including WFH explicitly in salary agreements would be unusual largely because workers incur a large number of other work related expenses that are not explicitly enumerated in the agreement. But those costs are implicitly included, as employers have to compete against each other to offer salary and benefits necessary to attract talent.

But practically speaking, it would not be surprising to see WFH companies offer slightly higher salaries largely due to the significant savings associated with no offices, as well as the reduced risk of not having a lease. If I save $27K a year per employee (from the article), I can easily offer candidates $10K more than my competitors with an office, increasing profit and attracting higher quality talent.