This isn't just an Illustrator problem. It is a problem among many CS apps, with no two of them having the same way to do the same thing to layers.
But I'll give some specific examples:
I don't care which way Adobe chooses. But please, pick ONE WAY for ALL the CS apps to work. A CS user should be able to learn one CS app, learn something like "I can duplicate a layer by right-clicking and selecting "Duplicate layer", and then be able to do that in every CS app. That would make it a real suite, and not merely a collection of different applications that can be bought at once.