With some qualifications, I have to agree with Duff's comment about the 'sitting through them again' notion being a contributing factor to a great film (I know, I know, good lord, something I agree with Duff on - shurely shome mishtake as Private Eye would have it!).
Nevertheless, I have to admit that I have gradually lost patience with worthy but dull stuff taking up my film-watching time (see here). To take a further example, I have a lot of sympathy with Norm's dismissal of particular works by Peter Greenaway (though not Greenaway's entirel output: I rather liked Drowning by Numbers and the documentary Act of God he directed about lightening strikes - a work that remains with me after all these years. And Cloud still likes Belly of an Architect with the magnificent Brian Dennehy).
Anyway, I digress. To return to the issue of rewatchability. I do think that great films are emininently rewatchable (though you have to take some account of mood). The difficulty is that I don't think the logic can be taken so far as to say that a film that is rewatchable is necessarily great (and I don't think that is what you were saying Duffman, before you get your panties in a twist again). Films can be rewatchable for all sorts of reasons, not all of them connected with such edifying sentiments as defining the film as 'great'. My friend has watched Gladiator more times than she can count, but is under no illusion that the film is 'great'. And though we cheered Rusty's Oscar win - for the circumstance as much as anything - she would have been much happier to see him rewarded for The Insider or LA Confidential.
The point is that some films can be like comfort blankets. Take True Romance. Cloud and I have watched that a ton of times. It makes us laugh, it makes us cry, it has thrills and vibrancy, a great soundtrack, and possibly Brad Pitt's best performance outside of Fight Club (I like Seven, but I don't think the performance was as good). I don't think either of us would place it on a great films list. But for us it is very rewatchable.
I guess what I am trying to articulate - as usual, very badly - is that some stuff is worthy but dull and only makes lists because some folk feel it should do. Some stuff is difficult and doesn't make for 'easy' viewing, but that's not to say I wouldn't acknowledge that it was great; just as I wouldn't claim greatness for a frippery such as If Only, even though I love the film with a passion. greatness can be an awfully subjective thing if we allow such matters as rewatchability to dictate the boundaries. But that isn't to say it should never be taken account of, only that we must beware of making it a dominant criteria.