Save Money on Painting

The following is from Noel Whittaker's newsletter. Does anybody know whether there is any validity to this?
"A painter was telling me if you washed your house down regularly, the paint
would last much longer. I’ve got a great big old wooden house and it only costs
me $250 to have it washed. When you consider it would cost over $10 000 to
paint it, that sounds like a good investment."

If you live in a high salt or industrial pollution area then the answer is yes. If it is inert dirt then the answer is no as the dirt stops some of the UV damage.

Mind you I'm not sure I'd want my IP's looking dirty anyway;)