> The bottom-up people [...] only add abstractions [later]

I don't think bottom-up verses top-down are like political camps. I think it's more innate, like right-brained vs. left-brained.

I can't understand abstractions till I first understand the lower level. I could never learn algebra without first learning arithmetic. (BTW, I'm old enough to have lived through the New Math philosophy which insisted that every grade school text book start with a chapter on set theory before moving on to, say, fractions.) This doesn't mean that I can't start with a functional model, but it does mean that I start with simple functions and move up.