I don't understand, how would SocialToo help the scammers? Seems to me if a scammer follows you and then unfollows after a week, it would be nice to have auto-unfollow. So SocialToo would help against the scammers?
Twitter accounts are blocked from following too many people if they have a high follower-to-following ratio, so in order to have a large audience, you have to keep this ratio closer to 1.
An 'internet marketer' will follow many people in an automated fashion. Some will follow them back - either automatically, or because the scammer is convincingly faking a real person. The ones that don't follow them back are useless to the scammer. He therefore needs to unfollow them - so he can drop his following-to-followed ratio and begin the cycle again. SocialToo (and many other tools) help with this by automating the unfollowing part of the process.
Promoting scammy affiliate offers through Twitter only scales to an interesting point through automation, so if you break the automation, you break the process. That's what I assume Twitter is doing. The scammers will eventually replace API-based methods with screen-scraping bots, which is what they use for other social sites around the web.
Why would a casual user ever want to unfollow somebody just because that person has stopped following? The only possible reason is to use that now vacant follow on somebody who's more likely to follow them back, which is the exact strategy of scammers taken to an extreme level.
Incidentally, if Twitter really didn't want people trying to game the system, they probably shouldn't have made the system so much like a game.
On the other hand, since I gave up on managing followers, I found that a lot of them sort themselves out by themselves: by the time I check if I want to follow them back, they have already been deleted from Twitter as spammers. Auto-unfollow could help in the same way, by removing those scammers who managed to evade deletion by Twitter.
Granted, I think Twitter frowns on auto-follow, too, but there are some valid reasons for it imo. Also in some cases it jut seems polite to follow back - think strange acquaintance from last party, if you don't have the guts to say "I don't really like you".