Zynga's business plan is a perfectly understandable one.
1. They see a product that works - they know there is a market for this product, with an approximate size of N.
2. They make a copy of the game, knowing that they'll capture 1/Nth of the market.
You can't say Zynga has no model or plan. Their power comes from crunching numbers, and monitizing the crap out of their products. If their competition is not doing that - it's certainly not the fault of Zynga. The long and the short of it is - companies are in business to make money. Zynga doesn't pretend to make games for fun, it's to make cash - and it obviously works.
If, as the nay-sayers say, all Zynga games were terrible, and poor copies of other titles - then they wouldn't be making money or headlines.
I don't care either way, but you have to acknowledge reality.