One idea. We need some form of crowd control. Here are means by which each class can ensure their target doesn't get away, by class:
Druid: Entangling Roots; Travel Form. (Faerie Fire, to prevent stealth.)
Hunter: Freezing Trap, Frost Trap (1 minute shared cooldown, reducible via Survival talents); Wing Clip (6 second cooldown); Intimidation (Beast Mastery); (Improved) Concussive Shot. (Hunter's Mark/Track Hidden, to defeat stealth.)
Mage: Frost Nova (30 sec cooldown); Cone of Cold/Dragon's Breath (30 sec shared cooldown); Frostbolt; Impact (Fire talent); Slow (Arcane talent); Polymorph. Blink (15 sec cooldown). (AoEs can be spammed to reveal stealth.)
Priest: Fear (also breaks stealth). In addition, DoTs will break stealth and ensure a slow, painful death for anyone who tries to run away.
Rogue: Cheap Shot; Blade Twisting (Combat talent); Gouge (6 sec cooldown); Kidney Shot; Blind (3 min cooldown); Sprint (5 min cooldown); Crippling Poison.
Shaman: Frost Shock (6 sec shared cooldown); Earthbind Totem; Ghost Wolf. (Some totems will foil stealth.)
Warlock: Curse of Exhaustion; fear and DoTs (see Priest).
Warrior: Intercept (requires Berserker Stance); Hamstring; Intimidating Shout (2 min cooldown). (Thunder Clap can detect stealth.)
Paladin: Avenger's Shield (requires 41 points in Protection--in other words, a non-DPS build); Hammer of Justice (1 min cooldown); Repentance (1 min cooldown). (Consecration can break stealth, but it is EXPENSIVE.)
Do you see now the folly of having a melee DPS class with only 2 CC abilities on long cooldowns (one of which breaks on damage, for Arathor's sake)? Compare the Paladin's CC with any other class and try to tell me we even come close.
Now, for a comparison of Melee DPS classes and their ranged abilities:
Feral Druid: Switch out of form to cast Starfire, Moonfire, etc.
Enhancement Shaman: Shocks; Lightning Bolt/Chain Lightning.
Rogue: Deadly Throw. Blind also has a 30 yd range.
Arms/Fury Warrior: Auto Shot/Auto Throw. Weak, but better than nothing.
Survival Hunter: I'm half-joking, seeing as how even a Survival hunter shouldn't melee unless absolutely necessary. But for the record, the pet can pursue the target or the hunter could actually use their ranged weapon (and shots)...
Retribution Paladin: Uh...Consecration has an 8 yard radius! And Hammer of Wrath! (Expensive as hell and can only be used against nearly dead targets...oh, and can be resisted AND can miss...don't forget the 6 second cooldown)
Yeah, so who gets the short end of the stick there? Warriors maybe, but they don't need mana (or rage, or whatever) to take an auto-shot at a fleeing target...