The purpose of boiling the rocks is to sterilize them so they are safe for your leo's cage. If you bring in something from "the wild" and just toss in in the cage, you're letting everything that's touched that rock/wood touch your gecko. Some bacteria LOVE to hang out on things an wait for days for something else to touch it. With wood, you could bring in all types of very small insects/parasites that would love to harm your gecko.
It probably only takes about 10mins to boil water, 5 mins to boil the rock and 15mins to cool it off, so 30mins isn't as bad as a vet bill or dead gecko don't ya think?
That's what I did with all my natural decorations. Soaked them in bleach overnight, then let them air dry. When bleach dries it turns to salt so no harm done.