Personally, I believe that a class based system like D&D, should have, you know, classes. I don't get the reasoning behind paring them all down to just three or four. Sure, I can build a fighter, give him some outdoorsy skills, and call him a ranger, but he's not going to have cool ranger abilities. Class based games give us a menu system with features created by the designers. This puts some limits on my imagination, therefore, the more choices I have, the more likely I will be able to create a unique character, or one closer to what I'm picturing. It opens up the game to more possibilities. It's easier to play with time periods, moods or other genres. As a GM, it's far easier to cut down on unwanted classes, because they don't fit the campaign, than to have to create new ones to fill up a "weird west" genre, for example. If your game suits a more down to earth feel, then you can remove the gunslingers, psychics, alchemists and puppeteers. But they are there for when games are more free wheeling, or have a specific feel.
On top of all this, D&D is kind of a crazy mash up of oddball rules, an ecology that makes no sense, with monsters everywhere and a strangely democratic medieval setting, where peasants are free to wander away from their responsibilities to become adventurers. Rangers that are more than skilled outdoorsy fighters, monks, New Age druids, dragonborn paladins, halfling barbarians, artificers, half-elf investigators...sure, why not?