Unfortunately, it's not that simple. While this might not be the case for all of the upvoting services, greedy robots are ran by greedy people. In case their services have to stop, they are likely to just upvote their delegators or find different ways of being selfish.

There are also ways of performing this service in a more "righteous" way, as clearly demonstrated by Hive account@ecotrain (although I'm not saying it's perfect), so you just can't blame the type of business in itself.