Just to clarify some things here that seen to be causing confusion.
1. Google has stated in the past that the cards based interface on attention critical interfaces (wear, glass, auto, etc) will be restricted to essential notifications. No ads. And I have to assume they'll take actions against apps that violate this.
2. I saw a lot of 4.3 as being the base Android version necessary for this functionality. This is likely because 4.3 was the first aosp version to support Bluetooth 4 LE natively, or really, anything better than BT1. It may be possible other manufacturers that built their own Bluetooth stacks (Samsung, HTC) may support Auto or Wear on earlier versions. Another requirement that I *think* applies is that 4.3 was the minimum version required for Google Now, which is undoubtedly driving all of this.
3. Development cycles are much longer than just a few months. Both of these companies have been working on this crap for years. Hitting a button and making an led light up is exciting and easy. Defining a standard, consistent public APIs, developing a developers testing and verification suite, and getting partners takes a very long time and quite a lot of work. The idea that any of this is a response to rumors of a competitors product just shows extreme ignorance to the process.
4. Google has been working on cards and Google Now for a while. Context aware PDA's, where the context is your lifestyle and behavior, are what's next and it works remarkably well. They announced this work many years ago. The Moto X was the first device to show it all of, it's over 1.5 years old and the features were rumored for years before it. Cards is Google's thing and it works. It's what's different.
5. Google has been getting good at notifications for a long time. I have to assume this is what led to cards. The watch, as a notification center and health tracking apparatus is a natural next step in a world with increasingly larger phones, not the least of which will be a 5.5" iPhone. Some will like watches, some won't. However a $200-250 price tag is gonna be much easier to swallow than what will undoubtedly be a $500 minimum tag on an iWatch.