Carbon Fiber is not a magic material and like any other material it is subject to failure. I would be curious see the actual percentage of CF bike frames that have failed compared to the number of CF bikes over 2 years old that are still on the road. As for the photos that you saw of the broken CF bike frames, you can do an internet search for "steel bike frame failures" or "aluminum bike frame failures" and most likely see just as many photos of broken steel and aluminum frames that have failed without warning.

Having read your post got me thinking since I also own a Colnago. I read my Colnago manual and there was nothing in it that stated the Useful Life of the frame and fork were only 2 years. In fact Useful Life was never defined in the manual but only mentioned to say that not following the manual to the letter will shorten the Useful Life of the frame. The only thing I saw that had anything to do with two years is the warranty. If they consider the warranty its Useful Life, than we all should be ditching our bikes at the end of the warranty period, regardless of the material used to make them.

On page 8 of my Colnago manual, item number 9, under "Actions/Inactions that can reduce the Useful Life or your Colnago frame:

"Use of the product by anybody whose body weight is in excess of 95 kg (209 pounds). If you are in this weight category, you will need to request that Colnago fabricate a frame proper for your weight."

Maximum rider weight is emphasized again on page 17. And I think this is why most of the sudden CF failures occur. I've seen some pretty heavy riders on CF frames. I'm 150 pounds and I've ridden my 2012 Ace almost 35,000 miles. I'm guessing it's way past its Useful Life.