QuickTime 7 DOES cache streams. Check ~/Library/Caches/QuickTime while playing any streamed media.
http://developer.apple.com/documentation/QuickTime/Conceptual/QT7UpdateGuide/Cha pter02/chapter2_section12.html
"Cache of a QuickTime audio or video file downloaded or streamed from the Internet; if the file was created with QuickTime 6.5 or earlier, it may be opened in QuickTime player if the file extension is changed to match the original file (i.e. .mp3, .mpeg, .mov)"
http://www.fileinfo.net/extension/qtch
(Note that the qtch format for QT 7+ is not the same and so far there is no pubicly known way to make the qtch files from QT 7 playable as movies.)
Prior to QT 7, "iGetMovies" could use the cache to grab the movie.
I haven't tried using QT Player 6 while QT 7 is installed to see what sort of qtch file is created while playing a stream...