sorry, I didn't mean to be sarcastic or imply YOU didn't realise that (that blogs are adverts anyway). Was typing whilst on the bus on my phone.
But I think I did answer your question, yes the trickle down effect to the smaller/mum/personal blogs is rapid, and no, of course the fashion houses don't know they exist, but any blogger interested in fashion will be aware of blogs higher up the pecking order, so to speak, and that is where they will take their lead from, and so on, all the way up to the brands and agencies in charge, who plan the campaigns in the first place.
As to how THEY (the men in black at the top) decide that culottes or dungarees will the be the next big thing, no idea. Science, just fancy a laugh, who knows? I believe there are some MNers who really follow the catwalks, fashion shows and actually know a bit about how the industry works, could actually be an interesting discussion (still not being sarcastic, and I can't do smilies).