3.4 OUNCES OR BOOM?

OK, now I am all for airport security but there is something that I don't really understand at all. I don't really understand the 3.4 ounce rule for liquids when you travel. I mean what are you going to do with 5.0 ounces of shampoo? Now what is even stranger to me is on my recent return from Peru. At the Lima airport I stopped by one of the Duty Free stores and picked up three very large bottle of Pisco (a very popular and potent Peruvian alcohol). Now you basically give the store your flight number and the bottles are then stowed away on the plane (or so I thought). Now right after I had taken my seat I hear my name being called. The flight attendant then hands me the three bottles of booze that I had just bought! Huh? Now I had assumed they would store these somewhere and that I would get them after the flight but this wasn't the case. So basically I had three very large bottles of some very potent alcohol in the overhead bin above my seat which was probably enough to make a nuclear bomb! Now tell me if this makes any sense whatsoever. Jeez......like I said, I just don't get it.