Why don't project 13 and 15 need a 5V power supply?

Hello everyone,
I've reached the end of the book of the starter kit and really enjoyed it. There are still quite a few things I don't quite understand though. I just wonder why project 13 and 15 don't need a 5V power supply? Is it because the external source (capacity sensor / pushbutton of a sound module) can supply enough power for it? Thanks!
Che Ong