The major companies that are reputable and recommended by frequent cruisers are: Access America, Travelguard and CSA (?). We have always purchased TravelGuard as it is based on our ages and amount of trip. Our primary medical insurance would be used first for any medical expense which is OK with me. Prices have been better than quoted through a TA. You can access their web site to check out their policies and features, too.
We had purchased Travelguard insurance when we booked a cruise on Carnival's Imagination Sept '99. Two weeks before the cruise my 80 year old mother-in-law became gravely ill and we cancelled. As it turned out she died and we would have been on the cruise if we hadn't cancelled. They gave us such a hard time requesting medical background on my mother-in-law. They were trying to say that she had a pre-existing condition. Of course she did. She had a million things wrong with her but she wasn't the one going on the cruise or the one purchasing insurance. We had to have papers signed by her doctors and it was getting ugly. I finally copied Travelguard on letters to the State Attorney General and the Insurance Commissioner and they finally agreed to let us book at a later date (which is what we wanted). I'm not singleing out this insurance company-they probably all operate the same way. What I'm saying is be prepared to fight because they sure don't make it as easy as their brochures have you believe.
Kelly's situation was hopefully an exception and very unfortunate. We purchased Travelguard and had a good experience. We were delayed debarking in LA on a Panama cruise and missed our flight. We had to stay an extra night in LA. United did not charge us any extra for changing the flight. But, Travelguard reimbursed us for incidental expenses as well as the hotel that night. We did not have any problems at all. Again, totally different situation than Kelly's. I'm sure as she says they all operate essentially the same way.
As Toni mentioned, we purchase within the time frame for the "pre-existing clause to be waived". We too have family that is older and one with a "terminal illness" condition. But she has lived 3 months longer than she was given! OK by us. I also buy it for all of the other coverage features, like airlines, delays, lost luggage and medical.