Do new wire runs in an existing ceiling need to be stapled down?

I've heard some people say that code requires wiring in the wall to be stapled to framing every so often (how often?), but when you are doing a remodel, is that necessary?

I have a two story house, and would like to remove one standard dome light on the first floor ceiling and replace it with 6 recessed lights. There is about 12" of empty space between the floors, and it seems easy enough to run the wire from light to light without cutting any drywall except for the 4-5" holes required for the lights. However, there's no way I'd be able to staple the wiring down. It's just going to be loose in the ceiling, running through a small hole in the I joists every once in a while.

They sell "remodel" light cans that are made specifically so you only have to cut a hole big enough for them to fit in, so this seems like a common job. What am I missing and how can I do this job in the most correct way?

This is in Dallas, TX, single family residence.