As I was working on a random encounter table, it occurred to me that I personally haven't played encounters against the majority of the creatures that ended up on the table. That realization set me to thinking about whether that's normal, and I soon came to the conclusion that if my experiences are anything close to normative, most people who play D&D 3.X/Pathfinder, even long-time players, may very well have spent a majority of their time playing encounters that only feature a very small subset of all that are available in the core rules (to say nothing of the dozens or maybe hundreds of creatures that have been included in various supplements over the years).
Virtually all campaigns I've played (as a PC, not a DM) have leaned heavily on only about three or four major types of creature: Humanoids, Outsiders (with pride of place going to devils, demons, and genies), Undead, Elementals and Vermin. I'd say that the frequency of my encounters against these kinds of creature is roughly in the order presented, as well. Dragons haven't been a huge feature of my gaming experience, and most DMs I've played under have been of the "Great Wyrm or GTFO" persuasion. I think that once or twice, I have played encounters against Aberrations.
But never an Ooze. Never a Plant (that I can recall), or ANY kind of Fey. No harpies, medusae, minotaurs, or any other Monstrous Humanoid (that I can recall). I'm not positive, but I'm actually pretty sure I've never had an encounter with anything with the Animal type. And I think my only encounter with a Magical Beast was an ankheg. I've played against Constructs once or twice.
I don't necessarily think there's anything wrong with that, but it did occur to me that I might want to see if I'm weird, or if this is a common experience for most people who play. And if it is a common experience, why?