In this case, it's not even his salary: it's his comfort and ease of labor.
It's hard to support a heterogeneous space of user agents running on a heterogeneous set of platforms. Eventually, abstractions break and you end up with a weird bug that only manifests on such-and-such browser in so-and-so configuration.
How much easier life is if you only have to support a few browsers on hardware that checksums to have a known-good configuration...