Almost any modern desktop you buy (heck even phone) has around 4 cores, it's been this way for years now. After that point the average user doesn't see any particular gain in adding more cores. An 8 core machine really only helps power users. Most users are not running hundreds of threads, look at most your applications, they may have any number of threads running, but only one or two are ever loaded with data. This is the serial world we currently live in.
I'd guess 2 cores is still the majority of machines being sold, though 4 cores is probably a close second by now. 4 cores was certainly not standard on the majority of devices in the last few years.
