Having not actually been to a Couples property yet, just booked for 2013, I feel a little weird giving my opinion, but from what I understand, the beach at CSS (where we are going) is kinda 'small', I for one, wouldn't like big beds blocking my view. Space wise you can get more loungers/mats in the same space as one of those beds. I also agree that people would be trying to "hold" them for themselves ... creating 'discord' among guests doesn't seem to be the way to go, but it's just my opinion.
I love bali beds at other resorts and have not found cleanliness to be an issue. They are easily covered with clean towels and our private bed has always been made up with fresh linens.
That being said, I do not think they belong at Couples resorts. There is already too much "saving" that goes on and this would be a recipe for disaster. Also, I would not want to see it become like the S resorts, with these designated for certain room categories only.
I would be happy if they changed the towel policy personally. I find it not in keeping with a resort at this price point.