As you go up in price/level the parts have less plastic and painted steel, more aluminum and plated steel, making it lighter and more likely to last. At the top level they have carbon fiber and titanium. Higher levels also have more ball bearings in the shifter pivots and derailleur pulleys. Lower groups have features that are a few years behind the higher ones. And you can just tell playing with the components there's an improvement in tolerances, fit and finish... Tourney feels like a Matchbox car and DA feels like missile gyroscope parts.