Here goes.
Fantasy RPG's to begin with were defined by Fantasy books of the day.
Sounds rational enough, right? The people who played fantasy were influenced by the big books of the day and earlier.
When was D+D first out? The seventies?
Right. Fantasy had been going much before that. Possibly due to it's extremely unknown subculture factor, people who liked RPGs were the ones that were deeply interested in Fantasy, and fantasy books in general. So we have some evidence of researching in our older patrons. Maybe because there wasn't such a glut in the market of pulp fantasy (I wouldn't know, I wasn't alive at this point) things such as the masterworks were able to be read much more.
So, these books were read by geeks and had a deep effect on games. This seems a fair inclination. Especially to start with. The good ole days when magic was rare and magical, monsters were new and dangerous and traps weren't simply assumed to be bypassed. Why? Because even this so called fire-and-forget magic of Vancian origin (If you read the books again) is quite amazing and different. (Read Sepulcraves Mostin the Metagnostic for a very good re-enactment of a Vancian wizard, at least the insanity.)
Cut to the current day. D+D is still a not-particularly-huge hobby group filled with geeks and fanatics. But it's bigger and it's more popular than before. People can pick up and play and enjoy games - and often do. But they don't need to be fantasy geeks to pick it up. In fact, they barely need be able to read at all. If they have read fantasy it's going to be the good fantasy of their day.
It's logical that if the books of elder year affected our elder, the books of today affect our RPGs. But thats a wrong statement. It's actually incorrect to assume this at all. If we assume modern authors to be Eddings, Lackey, Robin Hobb, Hickman and Weis for us geeks and so on - god, if we even look at those piss-poor D+D novels. Do our games resemble this? Everyone's game is different. BUT - the D+D "Core Setting" as I take it does not act like those books at all, especially regarding magic. New players are not as well read as older players because of the neccesity of old players to be more obsessive about fantasy (Needed to define it for themselves?). I have a good player in my group that's never read a fantasy book in his life. But he likes fantasy.
My theory is this - D+D over time has evolved its own sort of self-propagating stereotype. You can see this from Dungeon adventures. You can especially see this from the fact a 10 foot pole is standard equipment in a bog standard game. It's a stereotype that gamers themselves put forward, but it's there. It very much has traces of killing evil priests and taking their stuff, but it isn't taking a lot of the more complex issues raised in either the classics or Modern fiction in. Dungeon, the magazine that caters exclusively to our hobby - Does it deal with ignorant non-relativistic viewpoints as wrong as a general rule? Does it cover unknowable horror as a roleplaying stunt? Not very often, though Dark gods are common enough. Is there a great focus on this? Nope, not really - thats for the DM to use or abuse.
Nope. It gives us dungeons filled with goblins. I must admit, there's a few interesting dungeons and things lately. But generally, there's a dungeon and lets get people in it, looting away.
The self-propagating stereotype of D+D is it's very basic nature of a combat/problem game overcome with dice. You get a lot of D+D haters yapping on about this endlessly. But the very nature of this dungeoneering and general stereotype leads into a sort of Dungeonpunk atmosphere that absolutely permeates Dungeon. The artwork especially lends to this.
Now, I'm sure people will say the game is what you make of it. But look at the way it's set up and how Dungeon deals with how to play the game. It's a quick bit of investigation followed by combat and traps and underground passages. We can see the general feel of the standard gamer leaning toward this feeling - otherwise Dungeon wouldn't be able to publish itself.
Anyway, I think RPG's started with Conan and so forth. But due to the nature of the difficulty of intellectual matters, they kept the dungeons and the combat and the spunky women but lost the horror of things unknown. Modern writers haven't influenced this stereotype a great deal; at least not as far as I can tell. What was easy and good about the old novels was kept, even though now there's probably dungeons even Conan wouldn't recognise. The dungeons tone might have changed over the years, but it's still a dungeon.
Once, a group of frightened and drunk (White, Norman/Saxon) adventurers treaded cautiously through dripping caverns, lanterns held high and sword in the other. Now, red-metalled plate and indigo weapon carrying drow stalk through abandoned dwarven mines. Things are a bit more PC, maybe, but a ten foot pole is a ten foot pole.
It's up to the GM to give influence to his game - otherwise the influence will be the stereotype of a dungeon-hack. Simple as that.