An old-school analogy comes to mind. People used to BS in common space. But it was just BS. Decisions were made, or at least formalized, in meetings.
And this isn't just a one-off either, I've seen other people report the same thing consistently, where 'conversion' rates in response to even the most basic questions or asks are pretty much zero.
Because of that it's not immediately obvious that Slack should be no different than just asking a Linux question in some random FreeNode channel or whatever. That's actually a pretty big issue that doesn't bode well for the longterm viability of Slack, if (for example) it turns out that it leads to significantly worse organizational decision-making than email due to lower participation rates.