I am pretty sure that any "movie" that was directly imported by iPhoto from the few versions has always added the keyword "movie" NOT ALL and I have been doing this for years ie. smart album with keyword "movie". It is however useful to add some Filename rules to smart album to find avi, 3gp, mov, mp4, m4v etc. as really old iPhoto libraries (like mine) will not have a the keyword added as older versions of iphoto did not add this keyword and i am pretty sure that upgrading a iphoto database does not add the keyword for all file types especially old ones ;-)

I cant test this as I have a modern library which has imported movies and added keyword. I do not have my 2003-2005 and 2006-2008 Library with me as on "holiday" which has a ton of old formats in it.

PS. This was a hint that i submitted from back in the day when i was called savage ;-)