I think SO chat could be to irc as SO itself is to Usenet or Usenet-style mail lists. When I first started programming, I asked questions on mail lists. I learned a ton this way (perl-beginners was especially good), but some lists had a lot of rules and some very, very type-A regulars: no top posting, give exact error messages, read the FAQ first, etc. None of these rules were necessarily unreasonable or unfair, but there was an inordinate amount of time spent telling new folks all the rules they were breaking: "The boilerplate disclaimer at the bottom of your email is longer than four lines. Signatures and bottom matter may only be four lines or less. Do not write to this list again until you...." Irc in my experience can be similar (just a few weeks ago, I had someone barking one-word commands at me on irc, because I was asking a question incorrectly).

By contrast, SO is relatively frictionless. There is some fussing about tags and which site to ask on, but for the most part, you ask and you get an answer. Less rules. I suspect that SO chat could be similarly frictionless, in comparison to irc.