PopCap have a good approach to cloning. It's basically, we love seeing clones because we enjoy seeing good games made, it increases the market size and the bad ones will sink anyway. They're confident in their ability to make really game games that will sell. They're sitting on one of the most cloned games of all time, but still manage to make good games and make money.
People seem to get stuck on the idea that a good game is good because of it's mechanic. Therefore if someone uses your mechanic, you're stuffed. A mechanic is only part of what makes a game really good. It's a similar mistake to having a feature focus in a product company.
It has been fun to see all the riffing off the Threes concept over the past couple of weeks. And I'm sure Asher Vollmer and team will benefit from it all. There is more interest in all the games, they'll have extra ideas from the clones that come out, they find out for free some ideas that don't work. It will help them raise the bar on Threes and make it a better, more successful game.
Because of power law distribution,
"... the 100th employee at Google did much better than the average venture-backed CEO did in the last decade."
So even being late on a $1b+ company is better then being first on a $100m company but orders of magnitude. And it's not worth the opportunity cost of going after $100m companies.