If the instructions say "use 90 degree wire," that is a real hint that the fixture fot over 75 degrees using the largest permitted bulb, installed per instructions.
There is a lot of room for "professional judgement" as to just how far that hot zone will extend, depending upon the installation. What is not so obvious is that the fixture will also affect other thing that are close to it.
As an example, I would say that in the case of a fluorescent fixture in a drop ceiling, the wires only need to be 90 degree rated to the end of the whip.
For a recessed can in an uninsulated confined space, I'd want all wires in that space rated.
For a lampholder with a PAR or halogen lamp 'poked through' an outside wall, only the wires to the fixture need be rated.
I think these examples show how the entire installation is relevant. The instructions do not, however, imply that you need to run 90 degree wire all the way to the panel.
