I would guess that the "vast majority" actually take about the length of time listed on the "processing times" web site (give or take a month or two).
This forum is not particulary representative of the "vast majority". Most folks don't find this forum until something screws up on their application. I'd guess that the incidence of Name Check issues on this forum, for example, is way more common that it is in the normal N-400 population.
I know that had my application not been descheduled, I would never have thought to look up what "N-400 descheduled" meant on the web and would never have found this. At the time, my original interview letter came only slightly after the processing times site seemed to indicate. I was no where near panic until I got the "deschedule" notice.
What I'm trying to say is "look up the 'processing times' for your district office".
The other place to look is the last couple of month's postings on the "timeline thread" for your district office.