Yes it's the 3rd generation iPad, but Apple is apparently not calling it the iPad 3.
2S is logical, since it isn't a physical design change, just features. Nearly the same as what happened in the iPhone 4 to 4S transition. The number only changes when the actual design of the device changes, based on Apple's history.
However, it seems they are going towards a Mac based approach to naming this from now on... unless it is officially named the "2S" or "3" when it is released. Apple may just stick to calling them 3rd, 4th, 5th generation from now on so they are simply "iPads."