Except that liquid helium is a consumable part of an MRI. You can capture the boil-off (or at least try), but you are going to constantly lose some of that boil-off to diffusion through bag/pipes/pump oil/etc. So if the cost of helium goes up, the cost of replacing gas in these systems goes up as well. And that is the scary thought.

So let me get this straight. You want everybody in the world to carry around synchronized OTPs for every computer they could possibly interact with securely, and all servers to store enough OTPs for all their users, and then, as the OTP protocol requires, throw out the pieces of the pad you've already used? The whole point of a OTP is to deny any sort of pattern formation in the encrypted data due to patterns present in the key and the encrypted stream by making sure there is absolutely no correlation between the two.

Then there is the distribution question. How do you make sure both sides of the OTP are the exact same? Without using quantum encryption protocols (sorry, I don't remember the current distance restrictions on these), there is no known secure way to distribute OTPs short of meeting in person with the person you want to share a pad with, and then making two exact copies of the data.

I'll take Diffie-Hellman for now. If we reach a point where quantum encryption becomes ubiquitous (I'm not holding my breath), then we can talk about OTP as a serious option.