I largely agree with this. It's mostly nostalgia. And to be honest, I think most players my age and older (I was 14 or 15 when BG came out) are probably jaded. It comes with age and experience, and seeing a lot of stuff come out, mostly bullshit (like rise of DLC).
I think Origins is 130% better than BG in pretty much every applicable aspect, and I love it. I would say it's the better game any day of the week. But thinking back to my first playthrough doesn't generate the same warm fuzzies as thinking back to the days of getting up early before middle school to play games like BG (or Daggerfall, or Diablo). The successors to these games arguably improved them, but they didn't catch me at the same time and place, so they didn't grab me quite as hard.
I got into BW games (and cRPGs in general) with BG, and the nostalgia question is something I've wondered about in the last few years. So I've gone back and replayed those older games relatviely recently, and my "current" impressions are somewhat varied.
The first BG has not aged well. It's not bad, but it doesn't do much worthy of note. The overarcing story is reasonably good, but not fleshed out the way later games did, the characters (particularly companions) have...pretty much no depth whatsoever, and the game mechanics, UI and general playability are pretty poor.
BG2:SoA on the other hand, is still a great RPG. The playability issues with the first game remain (and some stuff such as high level mages become agonising excercises in tedious micromanagament), but the story and characters more than make up for it. The main plot remains Biowares best IMO - admittedly, that opinion might be tainted by my dislike of "you're the chosen one and last hope to save the world" stories that they have used in every game bar DA2 since then, but even considering that, its thoroughly engrossing - your companions, while maybe not as fleshed out quite as much as in the more recent games are still interesting believable characters, and the big bad is utterly phenomonal. ToB let it slip somewhat, but was still reasonably fun.
NWN...well, I never completed the OC when the game first came out, and I couldn't do so when trying it again. It is utterly god awful, with a pathetic excuse for a story and boring characters laid over a functional but unspectacular game engine. Good mods though...
KotOR I actually feel has lost some of its greatness. Maybe because I've lost some of my love for Star Wars (well, the expanded universe) due to the horrible mechanics of the setting, maybe because after all these years, the big moment in the game just isn't special anymore, or maybe just because it's been outclassed, but I didn't enjoy the game nearly as much as when I played it new. It wasn't bad by any means, it's still a game I would recommend people play if they like RPGs, but doesn't quite live up to my memories (KotOR 2 on the other hand, is IMO, the finest thing to come out of Star Wars since the orginal films...)
Jade Empire on the other hand, seems better these days. When I first played it, I was actually quite disappointed. I didn't dislike it, but it didn't live up to what I though BW were capable of. Now though, I consider it probably their second best game behind BG2. The game mechanics are resonable - combat can get a bit repetative by the end of the game and/or with mulitple playthoughs, but it's not bad by any means - but the setting is utterly phenomonal (and the fact that it's never been revisited is an utter crime), the story engrossing, and the characters interesting. And, much like BG2, the big bad is brilliant. (Actually, that's something I feel Bioware have really lost in recent games - really good villains. Nothing they've done in any of the DA or ME games can compare the Irenicus or the Glorious Strategist. Hell, even Sarevok was probably more interesting, despite how reletively un-fleshed out he was.)