[chrismcb]

The simple answer is, because that is what is being used. The complicated answer is there are multiple ways to do things. And just because you know one way doesn't mean you shouldn't learn another. For uploading files you say you need to use one of three things, until you need to upload a file somewhere that doesn't support those things. You just need to learn some of these technologies, without a frame of reference. Learn a technology to learn a technology.