country groups on Pay per Download plan tell us everything I guess.. Those country groups are used in most of Pay per Download plan by other file hosting sites too..
why ? , simply because you are likely to generate premium sales from the users of the mentioned top-level countries..
so, if your visitors are mostly from the A and B Country Groups, and if you are not sharing files in a competetive area and if you even own a site , I would definitely go with Pay per Sale.
so if you know your users profile, and don't think they buy premium sales, then go for Pay per Download plan
