A lot of people love monsters. Personally, I like reading bestiaries for fun. I can sit down with a Monster Manual, Fiend Folio, or Creature Catalog and read it cover to cover. I think Angela has MMI-MMV and has made noises about acquiring others.
Do we really need that many monsters, though? If so, why? I'm pretty sure it isn't for simulationist biodiversity reasons...
I'm thinking about this primarily because I've been playing a lot of Oblivion lately. Oblivion is a huge game. It has monsters, sure. Here's the list:
Animals: Wolf, Timber Wolf, Boar, Black Bear, Brown Bear, Mountain Lion, Rat, Dog, Mudcrab, Sheep, Deer, Slaughterfish, Horse
Monsters: Goblins, Trolls, Ogres, Minotaurs, Unicorn, Will-o-the-wisp, Spriggan, Land Dreugh (big crab guy)
Undead: Skeleton, Zombie, Ghost, Wraith, Lich
Daedra (extraplanar demon-things): Scamp (gremlin-guy), Clanfear (triceratops-guy), Daedroth (big croc guy), Atronach (Flame, Frost, Storm), Spider Daedra (drider), Dremora (humanoid demon guy)
There are some variants (Minotaur Lords, Headless Zombies, Goblin Shamans, etc.) but that is pretty much it. Most of the opponents are PC races (bandits, marauders, necromancers, etc.)
(Sure, I play with a mod that adds a few monster variants to the vanilla list, but that wasn't actually why I picked that mod... and I'd have been fine with the original list.)
The point is that I don't miss having every encounter be with a unique monster type. It is perfectly fine with me if I have a series of encounters in which I fight a bunch of different goblins or whatever.
Part of this is because the game does a pretty good job of differentiating between near-identical creatures. Differences in armor and weapons (and magic) used by a goblin can make a big difference (for example, a little guy slashing quickly and furiously with a dagger can be more dangerous than one with a slower sword that you can more easily block). Similarly, terrain matters. A bear attacking you on a road can be rather different than a bear attacking you in a forested area where there are bushes and such in the way... or on a hillside where you have to be careful not to lose your footing (all too easy when you get whacked by a bear). Sometimes a skeleton archer might be attacking you from cover (or in darkness), and it might take you a while to figure out where those arrows are coming from. The difference between that encounter and the skeleton warrior that you encounter in the ruins and lure into triggering a trap is enormous.
With good encounter design, and a system that allows you to take advantage of it, you don't need to generate excitement with wholly different creature types. There are certainly other ways.
Do most tabletop RPGs support this? To a degree. Part of the problem with tabletop RPGs is that you tend to have too much information and too much time to process it. In D&D, for instance, PCs and monsters tend to move efficiently - avoiding difficult terrain (if you even keep track of it) and attacks of opportunity whenever possible. If a PC knows that a monster has resistance 5 to his fire spell, but his fire spell does an average of 6 points more than his ice spell, he'll usually use the fire spell anyway. (Compare this to "Your fire spell does a bit more damage than your ice spell, but you know that these creatures are somewhat resistant to fire" - this character will probably use the ice spell.) Combat can turn into a tactical puzzle-game (like the wargames that RPGs evolved from) rather than something exciting, visceral, and chaotic.
I think that I've managed to totally obscure any point I might have been trying to make here...