I live 14 floors up not far from the sea and the windows here are self cleaning. A week ago they were covered in salt from the sea and now they aren't because it's rained since then. The rain caused a reaction to occur with the salt to clean it off the glass and hey presto, self cleaning glass. It's rather like WFP but without the WFP.
I live in a mid terraced 3 bed house with 18 year old double glazing, not self cleaning, but a similar thing happens. Obviously not with salt as I live inland, but general dirt buildup. One good downpour and most of it is gone. Never looks like a proper clean with WFP though.
My experience with self cleaning glass in my area is that it turns grey with broken down dirt that doesn't get washed off because most of our rain is not heavy enough and upper windows are partially shielded from any rain by the roof overhang.
As far as cleaning is concerned I just use pure water, hot or cold to good effect.