This is common in very large guilds such as yours, Darr. Guild chat becomes almost like wow powerleveling general chat when you don't really know who half of the people in your guild are. How many times do you go out of your way for someone who's asking for help in general?
It's also common for cliques to form as people find others in the guild they get along with. In a large guild, you're definitely not going to get along with everyone. This doesn't have to be a bad thing. In fact, it probably prevents some drama. The people complaining about this situation are probably feeling left out, but that's a topic for a whole other column . . .
My guild isn't exactly small, either (150+ accounts with tons of alts). And every once in a while someone complains that no one replies to requests for help in guild chat. When I hear these complaints, what I recommend they do is to ask people in whispers rather than in guild chat. For one thing, people tend to ignore guild chat when they're focused on something. Also, people sometimes have the mentality that, in such a big guild, someone else will surely step up.
To me there's a vast difference between asking in wow powerleveling guild chat and whispering someone. In a large guild, asking for help in guild chat is almost like begging for change on the street. You're not asking anyone in particular. You're just hoping that a kind-hearted soul will notice you and help you out. There's something mildly undignified about it.