The other thing is IRC is one of those things where instant feedback isn't guaranteed. So many /join, ask a question, and /part by the time I even read it. In those cases, there's StackOverflow (and to a lesser extent reddit), where a thread is created and upvotes help a post weigh upwards a bit longer. As icing on the cake, there's nesting / voting in the conversation, as well.
With IRC, messages fade away and its really a matter of timing you find someone with the right expertise that bites. If you ask something at the wrong hour, you have to hope someone reads far enough up to answer you.
On StackOverflow, people are very generous in pointing to a newer answer with less votes. It's easy to copy and paste code snippets. Posts can be edited. StackOverflow posts are also more persistent as there's a concept of duplication and trying to have one thread for a question.