I don't know how sophisticated those dog's noses are but I would think that if my son was missing and the last place he slept was on the sofa under a rumpled blanket that would be the last place I would plant myself on. I don't know how many times I've heard 'don't touch anything, leave everything as you found it' from TV shows. If LE had already determined that Dylan's scent wasn't there or not strong enough then IMO that means the bed stuff has been left there ever since Dylan disappeared and that makes me believe that MR may not be fastidious on his housecleaning which makes me think that the bowl, spoon or anything else Dylan handled would probably be laying around so why didn't LE find Dylan's scent so the dogs could track him?
BBM
In the article linked below, it states:
"Police and volunteers searched a Colorado lake for a 13-year-old boy after cadaver dogs picked up a scent that led them to the edge of the water."
"Seven divers from New Mexico State Police searched Vallecito Lake through the weekend after the dogs followed the scent to the lake, according to KMGH."
http://abcnews.go.com/blogs/headlines/2012/11/lakes-searched-for-colorado-boy-who-vanished-during-dad-visit/