The difference between IRC and everything else is the organization of it all.
It's hard to track and organize real-time conversations.. they start off in one place and end up in another. And then even if that's fine, it's impossible to then categorize the results in any meaningful way that makes it easy for others not a part of the original discussion to go back and view the details of the (large) conversation.
The nature of emails and other "turn-based communication systems" makes people tend to make each individual "element" of the thread a standalone entity. A single has way better odds of making sense on its own than a single IRC message...
It's hard to track and organize real-time conversations.. they start off in one place and end up in another. And then even if that's fine, it's impossible to then categorize the results in any meaningful way that makes it easy for others not a part of the original discussion to go back and view the details of the (large) conversation.
The nature of emails and other "turn-based communication systems" makes people tend to make each individual "element" of the thread a standalone entity. A single has way better odds of making sense on its own than a single IRC message...