Slightly better base stats?
Melee champions and bruisers have some of THE most insane steroids and free stats in the game.
Take Miss Fortune. Her W active gives her 60% atk speed for 6 seconds, and (at Five Stacks), 30% of her ad is dealt as bonus magic Damage.
Now look at Olaf. His W gives him 80% attack speed, 21% lifesteal, and enhanced healing from all sources for the same amount of time. He also gets 1% atk speed per 1% missing health. He also gets 30 Bonus armor from his ult passive, and when he activates his ultimate he gets 80 AD and immunity to all CC for 6 seconds. And a 70% movement speed boost.
Tryndamere gets a free phantom dancers worth of Crit for attacking things. He also gets 25 free ad all the time, and up to 35 more ad based on missing health.
Darius gets 200 ad for stacking bleed on someone. he also gets 25% armor pen at all times.
So yeah, theres huge tradeoffs for picking a ranged champion. It's not flat across the board (like riot arbitrarily saying melees do 20% more damage to structures), but if you look, you'll see that melee champions are compensated.