i don't really think this is a new tip...we learned this in beauty school. We never put shampoo on dry hair, because I was told that the hair had to be wet so that the product could penetrate. perhaps i was wrong
but we were definetly taught that you only shampoo your scalp, and then let the suds run thru...
as for conditioner, I don't believe that you shouldn't condition your roots. i think it depends on your hair type. If you have thick coarse frizzy dry hair, you need conditioner all over. as far as build-up is concerned, you should be using a clarifying conditioner occasionally anyways. if you have fine, thin hair, then you definetly should condition your roots because they don't need it, and it would weigh your hair down, causing it to look flat and volume-less