The category is desktops or portables. Mac mini, iMac, etc. are Mac models, not categories. It's obvious that Apple sells far more notebooks than desktops, so it's also obvious to a moderately informed observer that the Mac mini is clearly not Apple's number one seller. You are simply misinformed, having drawn conclusions from incomplete data provided by third parties who are not privvy to all of Apple's sales information. While the Mac mini may be the top seller by a particular retailer, that does not mean that it is the number one model sold worldwide by Apple.
To put an end to this nonsense:
Phil Schiller, Apple Senior Vice President, Worldwide Marketing
Apple Special Event - October 23, 2012 at 15:36 into the event.
At about 26:51 into the address, he also states that the iMac -- not the Mac mini -- is the #1 selling desktop in the U.S., and that's not just Apple's #1, but the #1 selling desktop of any brand in the U.S.
AMEN. Now everyone let it go, 'cause it's 55 minutes until noon ET (9am Pacific) and we should be all about peace and love and good happiness stuff by the time the Apple store refreshes to show us the new mini, which will not be Quietly Let Go, because I Want One And Apple Knows It And They'd Never Do That To Me. =)