Note: In this thread is mostly about the PvE community, as there wasn't much of an established PvP community in Vanilla. I'm sure parallels can be drawn, but I'm not much of a PvPer myself, so hey.
Now I'm sure that every person that played the game in Vanilla has SOMETHING they feel nostalgic about. For me, it was running to Ironforge from Wetlands for the first time. For others, it may be the glory of finally having saved up enough for their first mount, or perhaps getting a legendary (haha yeah right, unless you were a guild leader).
The one argument I constantly see people go to though, whenever someone brings up the "rose-tinted glasses" and nostalgia, and particularly when LFD is mentioned, is that the "server community" is gone. "I remember in the good ol' days," they would say (I'm paraphrasing a bit of course, so bear with me), "when if you were bad, you got a reputation for it. If you were a jackass, nobody liked you and you didn't get into a group!"
"These days," they say, "you can be a total moron and not have to worry about any reparations. You could be a total tool and you'd just be able to re-queue and be able to be a jackass to some other unfortunate group."
I find that the community IS still most definitely there. However, it isn't in the same form exactly. To be precise, I should say that one isn't "forced" to participate in the community. Now recall, if you will, the days of yore, when there was no LFD. To do absolutely ANYTHING in the game required spamming in the LFG channel for hours. If someone with a bad rep whispers you, they get ignored. It's the exact same these days. The only difference is, it's only with raids now.
Now I play on the server Kil'Jaeden-US. It's a fairly large server (population of over 10k, according to wowprogress). It's ranked number 5 PvE-wise in the US. It's a big server. Now on this server, the raiding community is still fairly large. Maybe not as large as, say, Illidan, but it's big. Even in this large raiding community, everybody knows who's bad and who's good. In most cases, it's more of a guild reputation thing. For example, if you see someone from Stage Clear or Huge in Japan, they most likely know what they're doing. Then there's guilds like Req, where raid leaders will double-check your raiding credentials before inviting you if they see you're in that guild. However, there's also players that get a rep. Usually it'll be a guild master of a good guild that gets a good rep if he distributes loot fairly, is good at his class, and keeps the raid moving. Then there's players that are so bad, that they become notorious. People will KNOW if you're a bad raider, because the raiders know each other. When someone gets an exceptionally bad raider in their group, they might tell their friends, and word gets around.
Now the difference, as I said, is that you now have the CHOICE to participate in this community. For casuals that only do LFD, LFR and dailies, you guys don't need to participate. As a matter of fact, you really CAN'T participate in this community unless you're a raider or at least in a raiding guild. Most players won't participate in this community, because a larger portion of the WoW population are casuals. And this is fine. It's okay to be a casual. It's okay to not participate in the community. People may complain that there isn't a community for LFD/LFR, but let's be honest here: how often do you encounter things that problematic in LFR? And you won't be doing heroic dungeons forever, either.
To wrap it up, what people need to realize is that the community is still there. But in order to be part of it, in order to see it, you have to actually participate in it. Now I'm sure there's also communities in other areas. There's people regularly trolling in Trade chat, there's always those multi-boxers that go around Halfhill killing everyone. But I think that the community that people "miss" about the old days is the raiding community. It's still there. You just have to participate.
tl;dr The old WoW community isn't gone like everyone says it is, it's merely narrowed itself into the raiding community.