For some and growing population, keyboard and mouse is a compromise for interacting with a computer. Some work processes are faster or just more fun to do in "iPad mode" compared to "mouse and keyboard mode". Bring a cMP or even and MBP to bed or sofa for some gaming, watching movies, e-mailing, paying the bills, shopping, creative work is cumbersome compared to an iPad.Why would someone want to inconvenience themselves by only using an iPad? Life is too short to compromise.
The taste is different and the ability to chose computer after preference (iPhone, iPad, laptop and desktop) and user requirements is welcome. We have been force-fed with ill fitting, one size fits all idea of what a computer is for decades. An idea often dictated by the tech savvy without any thought of a wide user base.
Remember that 30 years ago a PC was considered a toy for those who program and run mainframes. Those where the days when an "app" was called a "program" and I do not miss it one bit.