@ theluthier, I’m sure there is a good reason for that 😉 Maybe it’s standard practice?
Anyway; @duerer and @theluthier : in the video it doesn’t make a difference, while there are no colors used in the Colorramp 🙂
Here’s an example with two colors that both have a Value of 1:

Here’s what OSL uses for Luminance:

As you can see, if R, G and B are all the same, it doesn’t do anything, but returning the value of R, G and B, or one of them, as they are all the same:)