It was a wild ride checking some of the winners, it turns out that people really have a twitter account to apply for anything they can win. Like all those "tag 3 friends and retweet this and reply under this post and you can win something!" type of things, few of the accounts have like multiple times a day done that and that is really interesting to see. Does it really bring in enough money to justify such amount of work?
Maybe when you streamline the operation it may not take that much time, but to me it looks like a lot of work to begin with. In the end congregations to the winners, they deserved it and duelbits is a king for doing something like this for customers.
That previous drawing contest has only few participants and most of the entry is just a doodle using a paint tool software. I believe only 1 contestant hand drawn a decent entry so I guess the contest is not a wild ride at all.
I think you are talking about pure giveaway with simple rules of retweeting and tagging a friends. Theres a lot of bot account user in twitter that abused giveaways of different casino. Its not a big a deal for them to do that but youre right that its somehow hard to do if you are not spending much time on twitter.