? I thought the published comparison tables also had the cases with different dimensions to allow for this. Have I misunderstood it?

Paul, I think you and Rob are saying the same thing, you're just saying it different ways, and you're misunderstanding each other's intentions. Something about the phrasing is tripping you up. You started by saying "The cases of the 40's will be bigger" but Rob thought you meant, "The cases of all the units will be bigger to make room for the 40's", even though I know you know better than that.

For everyone else's reference, here is a concise description of the situation as I understand it:

The 20 and 40 karmas will have two different size cases to accommodate two different size drives. Therefore you cannot put a 40 in a 20's case unless they come out with a physically-smaller version of the 40 gig drive in the future.

The beta units to which Rob was referring are 40-gig-size plastic which happens to have a 20-gig drive installed. I'm not sure why they did that for the beta units, but that's the current situation.