So are yous guys saying that by only watching subs you can learn Japanese? I don't think you are but is that it?
You can't learn a language by just watching a show, anime or not, sub or raw.
But it does help a lot if you're learning it at the same time (that's actually a really nice experience... I remember that when I learned a certain grammar point (it was the "-ta hou ga ii" structure), I kept hearing it afterwards. It's not that it didn't exist before, but that I never noticed it until then).
It also helps because it gives you an opportunity to hear the language, which is an important part of the learning process (not only with Japanese : you can do that with any language, just find some movies in their original versions)
It can also help with vocabulary, other than "kawaii" and "niisan", but for that you have to pay close attention and focus on learning new vocabulary, not really cool if you want to enjoy the show. Though the best way, for me, was to watch raw with an electronical dictionary : try to understand and quickly search new words when they're too important in the sentence that you can't skip them. This requires a certain level of understanding though. But you can be sure some of those words will be stuck in your head for a while, especially if they're repeated a lot (I learned all my police-related vocabulary by watching Detective Conan with this method), and thus will be easy to remember.
A good way to get better when you're already fluent enough is to do the subbing yourself :D