I've noticed something, and I think this is the main reason why, as pupils of CLI, we should have multiple sources for studying. I've noticed that in the follow-alongs, some books will omit a command here or there. They may be insignificant commands, like "no shutdown" or "clock rate xx000", but I've found that videos are a lot better for this because you can re-enact exactly what the instructor is doing. This doesn't mean that I'll toss the books, but hold on to them for better elaboration of a subject.

Edit: Also, I would like to add that certain commands on actual routers aren't available on PT... Which is why we have GNS3 for almost REAL routing.