Generally speaking - this reflects poor balancing on the part of the developers.
Some Examples
+In WoW as a ranged dps you can cause more damage from a safer distance, fight in more senarios, launches better ambushes, evade more danger than most tanks can take, and prolong a fight almost indefinitely if you need to buy breathing room for the healer.
+As a melee dps you can open the start menu, select "logout" and roll a ranged dps instead. (And before I start getting rogue-hate, a rogue is a ranged class where YOU are the bullets. Stealth-stun-stab-runaway-repeat. There's about as much actual "combat" as armwrestling your girlfriend)
+In Jade Empire, you
had to pick the sword because the spear was completely useless and ONLY there to give variety to the enemies.
+In KOTOR, you had to be a Jedi Guardian because you only got half the force points of your other full-jedi party members.
You'd be suprised at how little it's actually your own personal faults/quirks that define playstyle in games like these.