FAST does refresh fairly often. Seems like they are on a two week cycle. I have had sites get listed in FAST in that period of time, while at the same time all the others took much longer.
Sometimes they do not seem to update, or only do very small updates for a couple of months. Also some sites submitted just seem to take a very long time to get in FAST and there seems to be no good reason.
When they are active they do seem to update quicker than the rest so I guess they have a reasonably valid claim.
As you can see, they claim to have the freshest search on the web, not the freshest search results. Freshest search could mean 'The freshest search software' or 'The freshest search algo' or 'The freshest way of search for users' ar whatever ;-)