S'mon said:
Is this a modern or generational phenomena? I don't remember anything like it in the '80s, when I got into RPGs (AD&D, Star Wars d6, Paranoia et al). I suppose you could say I was a 'fan' of my favourite games systems in some sense, but nothing like the uncritical appreciation of say TSR or WEG that seems associated with the fanboy concept seemed to exist in the hobby back then.
Well I'm guessing I got into the RPG scene at exactly the same time you did more or less (sounds like we're talking later half of the 80s, no?). There was fanboyism then too, there's possibly more now, because there's a deeper rift in the psychology of gamers.
This is shown in the big three companies: On the one hand you have the comfortable majority of gamers, who are into D&D/D20, and like a kind of "standard" play.
Then there's the White Wolf crowd, a definite but sizeable minority, who believe roleplaying has to be "deep" (which is often synonymous for pseudo-intellectual and angsty), and the "fanboys" therein despise D20 as the "top dog". Those are not ALL WW fans, the "fanboys" are basically the contrarians who got into RPGs in the first place because they're a subculture, and now they want to be in a sub-culture of a sub-culture, meaning that D&D is WAY to mainstream to be "deep" in their eyes.
The third would be the Palladium crowd, which has a disproportionate crowd of fanboys. Interestingly enough, most people who play other RPGs tend to dislike the Palladium system, and some dislike Palladium itself because they were either burned by Palladium's practices as a company (late/never releases) or Kevin Siembieda's personality in particular. But the ones who are with Palladium and loyal to it are often rabid fanboys in that they will play almost nothing else. Palladium is on the other side of the spectrum from White Wolf; its still playing in the 80s, with a real sense of powergaming being just fine, and realism not being as important as huge guns. Whether the powers-that-be like to admit it or not, its also staying around because the rest of the RPG industry abandoned that sort of play, and the people who like it, and in the process lost a lot of younger roleplayers who were originally attracted to that kind of play.
I'm no Palladium fan myself, but I've always said the industry could stand to learn something from Palladium about how to recapture the "lost generation" of 12-15 year olds to turn around the decline in the gaming population. I think the industry has more to learn from Palladium than from White Wolf, frankly.
Nisarg
edit: I forgot to mention the one other class of fanboy, the "miniscule game no one has ever heard of" fanboy. These are possibly the funniest kind. They will go on boards and insist that "Obscurity: the Obscuring" is the best RPG in existence even though it only sold 2 copies and no one plays it besides himself, the author, and the author's dog Nigel.
One can include in this a few variations, like the Forge fanboys, who think RPGs like Sorceror and My Life with Master (?) are the future of gaming and Ron Edwards (designer of Sorcerer) is the most brilliant mind ever in roleplaying who will lead us all to the promised land; and the "Nobilis should replace Amber" people at the Guardians of Order Amber forum, who feel that replacing Amber Diceless Roleplaying's original rules with the Nobilis rules-set would be a great idea, even though Nobilis has only been a minor success in the industry for about the last two years while Amber is the most successful and long-living diceless RPG in history (with Amber-dedicated conventions in like four different countries to boot).