Hi Richy
There are some, but not many people who have been able to make a good living from pressure washing alone, most specialise in certain areas and so can command a better price for their services, other (like myself) have diversified and do lots of different things.
The problem with the term 'pressure washing' it summons up images of patio and drive cleaning and not everything else that can go with it.
I have been fortunate enough to get a couple of decent contracts that see me through the winter (commonly a quiet time for this activity) and make up the slack with the other things I do.
Not sure if this has been a help, but it gives you another point of view at least.
Andy