Ach't you just haven't ridden the right stuff. It is a bit different, the thrills come elsewhere and a big part is the satisfaction of completing something, its easier to quantify than mountain biking. Its easier insamuch as you can minimise the damage, I reckon mountain biking requires more short sharp bursts whereas road riding you can develop a high cadence style. Modern bike with relaxed geometry and a compact chainset means you can go as hard or as light as you like.