This is a kind of a guest post from my better half, adapted from a conversation we had earlier upon seeing the LPC message from Justin Trudeau in his khaki T and cargo shorts:
You want to counter the whole idea that Justin is the son of wealth. So you put him in his backyard or someone else's back yard dressed like a common person. You want him to look like the guy you could invite over to a BBQ, and contrast him with Stephen Harper in an ugly suit. That way you pull in NDP votes and the votes of guys who want the PM to look like "someone normal".
Just to add to the dear wife's comments, I'd say Justin looked like half the guys in Ontario this weekend, including me, and its easy to imagine having him over for a few beers. This guy...not so much.