Pretty funny, isn't it? I grew up with 2 x 5 "10 speed" - usually my standard utility rig was 42 x 52 with 14 - 28 5 speed cogset. I've got a 9 speed that's got 42 x 52 with a 30 inside, and a 12-28. Surprise. I'm almost always double shifting the back. Makes me wonder why I'm carrying those extra cogs! That bike has bar ends. I flipped the rear shifter to friction and in about 5 minutes forgot I'd ever had indexing. Weird.
Although riding hard and fast, I find the 10 cogs on my sport bike to just about right. Kind of a different environment and approach.
Too hilly for single speed, but it would sure make decisions easy.