I've got an interesting question and sorry if it sounds immature or just plain dumb. What makes a stem so complicated? I mean certain components I can understand the variety in price and performance, but I just don't understand the affected performance improvements of a $200 stem over a $20 stem. I can go as far as understand possibly weight shavings, especially those with a longer reach who can benefit a weight shaving at 140mm. Now I know material will have price variances, but in the end, what mechanics does a stem provide that would persuade your wallet. Is it stiffness? Looks? Weight? Name? Build quality? Don't mean to be ig'nant just want to know as I'm looking to purchase a new stem.

edit: also what's the difference between a 'track' stem vs. a 'road' stem? is there?