I've received my pre-departure guide for my cruise, in just over a month, and the only thing they mention supplying are rubber boots. They give suggestions for what to bring, which includes wind and waterproof outer layer.
I've just been 'chatting' with some friends who wanted to go to Antarctica and they said they can't get insurance (not sure can't or prohibitively expensive) due to pre-existing conditions. They're still under 75, but getting close.
Qantas doesn't charge extra. It's expensive in the first place, but with no extra charge for a cruise, it has worked out the best for my upcoming Greenland cruise. (I have no pre existing conditions).