The popularity of rainbow decks increased ten fold after this forum was opened and Scaredgirl disclosed his (her?) deck, that is true. People who read the previous forum were aware of rainbow's capabilities mainly due to Cisco's posts on his success rates which I think were pioneer, but it was only after Scaredgirl made his (her?) post that things took off.
The underlying reason for such popularity is not, however, only due to the fact that it obviously works, but also to the fact that more and more people are quitting experimenting with the game and coming straight to the forums seeking for easy advice. This game places a huge barrier on experimentation by having such high card costs for the new players, and doesn't take long for them to realize its pointless to keep restarting every time a deck sucks. I'm not even speaking about upgrade costs, I'm speaking about simple cards, the cost of building a simple good mono-deck which requires lots of card buying is quite high, specially if you keep experimenting (changing) your deck often. The cost of changing deck colors entirely hovers around 1200 electrum, which for newbies who play level 2/3 AI is is a lot of investment. Even the fact that the trainer URL is public but not divulged on the game itself is a bizarre barrier for newcomers.