Copy a good idea is of course what a big part of the web is made of.
But IMO, the reason why there are so many contests right now is because there is
a market. I mean that many webmasters want to play SEO contests. SEO contests are not real life SEO, however SEO contests are unique opportunities to test SEO techniques.
Real life SEO if boring. You can't really test more than the "the missionary position", because you can't offord to take risks with a serious site. With a contest site, you can try everything. And if the blacklist is what you get, so what... it's just a contest site.
At least that's why I'm playing
