It's because it's how the game is. It's how Icefrog and whomever he talks to wants it to be. It's not overpowered, it's part of the game, and most people enjoy that diversity.
You want a game full of 100 hero's who get the exact same upgrades from items? Homogeneity is bad
Charging money for DotA when DotA, itself, is free was never going to work.
And, as Lysah said, they tried to compete with a game people were already playing and had bought(WC3) and HoN wasn't much better. DotA already had a community, and HoN's community and infrastructure was crappy.
I am in love with playing Broodmother, his ability to control an entire lane with exceptional harass and burst damage with his ultimate is extremely fun. Also using his Spin Web ability to de-forest just in case ganks come about makes her all the more playable and don't forget her ability with a fully upgraded Spawn Spiderlings to create an entire army. If done efficiently and with enough spiderlings you can surround your enemy with your dozens of spiders so they cannot move, pop your ultimate and you're on a joyride or you could use those spiders with decent micro to jungle for you.
So much fun @_@.
So, how is the Sniper? Balanced or overpowered?
You've got 800 health 22 minutes in, if any of them even considered buying dust, your streak would have ended.
Sniper isn't bad, with items he is one of the worst carry heroes to deal with because the absolutely massive attack range of take aim allows him to attack from completely outside a team fight and the ministuns from headshot can actually lock down a hero completely, much like a ranged and target focused battery assault. I've stood toe to toe with Lycan late game and won because he just had a hard time attacking through headshots.
Unfortunately for him, he is one of the easiest to gank, even easier than Drow, and his damage does not scale like hers does, so he has a very hard time farming. People are just about forced to go mid him, utilizing take aim to farm the river from tower range, however, high picks like NS completely counter Sniper in this regard.
Some homogeneity is required if you want a game to be balanced because there has to be a baseline that everything operates around. Tiny's scepter upgrade is currently WAY above what others get from their scepters, so it needs to be cut down to size, or others need to be brought up to its level. Tiny's scepter essentially acts as an upgrade to his ultimate like other skills, but it also essentially gives him a free Battle Fury on top of it. Tiny's ultimate gives him huge attack damage and bonus damage to Toss; why does his scepter upgrade give him cleave in addition to bonus damage (this time vs buildings) and bonus Toss damage?