The "problem" is that they WANT to use the extra remote storage, with a UI as good as DropBox's and consolidated with the other stuff they have on DropBox, but can't because they don't have enough local space or don't want to sync all their remote storage to every machine.

It is true that in some cases they may not have realized they had this desire until ExpanDrive gave them enough storage to think about it, but they do now.