It's not stupid at all. Why would you waste time doing a screen shot and sending it to Photoshop when you can just enlarge it with a magnifying glass or loupe? It works very well.
I'm sorry but to me, it is kind of dumb... It's not like those icons were hand-painted first, there is no needs for "screen shots". I mean, you're working on a digital platform (so no needs to do any screen shots or print out), when you can just check at the real (original) thing in any size you want.