I presume that when the original developers were casting around for a name, they thought about people who Draw Up designs but changed it from DrawUp to SketchUp. Maybe that happened because of the humour in having it sound like a well known variety of tomato condiment.
Ironically though, one of the things you can’t easily do in SU is to sketch. For a building designer, that is a major drawback. I bet many of us still start with pencil and paper. But pencil and paper has the drawback that it is very difficult to be sure you are drawing anywhere near scale. When you transfer sketches into CAD, you often find they don’t work the way you had hoped. There is a gap in the market here, surely?
There is some very good sketching software for iPads aimed at artists and graphic designers, but what I hanker after is some hybrid between full blown CAD and a simple means of electronic doodling - something that allows you to design in a loose and fluid way roughly to scale and then be able to transfer the end result to a CAD package to work things up in detail. Or maybe someone knows of a package to do just this already?