So everybody doesn't have to go watch it, here is a shortened version of what Steele said in the video:
Although Fortress is originally designed as an object-oriented framework in which to build an array-style scientific programming language, [...] as we've experimented with it and tried to get the parallelism going we found ourselves pushed more and more in the direction of using immutable data structures and a functional style of programming. [...] If I'd known seven years ago what I know now, I would have started with Haskell and pushed it a tenth of the way toward Fortran instead of starting with Fortran and pushing it nine tenths of the way toward Haskell.
I think I might use this in some slides soon. :) Thanks for pointing it out! - Jake