Kinda looks like a doubling every two years-ish, no?
Yeah, but they're not reaching the stores as fast as they used to... I still can't find any 4TB HD at my usually retailer, and the prices of 3TB HDs are still quite insane.
With Bitcoin there is no fixed transaction fee, miners can charge whatever they want. So if a miner charges you 100 BTC to send a transaction then you have to pay. Luke-jr is currently doing this with coiledcoin, so it's not a theoretical thing, it's actually happening. Anyone can mine but if you don't have enough power it could take you 5 years to mine a block and not be charged 100 BTC. So if your life savings are less than the transaction fee then it's essentially like losing your life savings if you ever wanted to actually spend them. This isn't true right now in Bitcoin, but it could potentially happen because transaction fees in Bitcoin are not fixed.
Miners are also users. If they can't use their BTC (can't even withdraw them, actually) because the pools they use has fees far too high, they'll switch to others, obviously...