I think this is just so that Amazon can avoid permanently storing data from idle accounts which are within the free-storage quota. It really ought to be better clarified, though.
Perhaps, but it's pure laziness. Amazon should simply archive the data if they want to free up capacity on their SimpleDB servers. I can't imagine SimpleDB's servers are struggling under the load of their dozen-or-so users.
Maybe so, but the obvious solution then is to give users an option to disable the free portion of the service. Disappearing data ain't worth the $25 a month or whatever you save with the free usage.
So long as I'm paying for the service and storage, stay the hell away from my data!