Hi Mark
I don't see how misleading the customer by stating hot washing gets better results than cold is a good thing. These folks who have advised you to do this are possibly going to actually lose customers if the customer finds out that in fact a cold wash will be just as good. Not for doing a bad job or being too expensive, but simply for not being truthful.
There are however instances when steam will be useful; for instance when you have oil to remove, but as a general thing I only use steam for gum, graffiti, smoke damage and paint removal.
None of my customers have ever expressed a preference for a steam wash of their driveway or patio.
If you have the money to spend then it is a good idea to have the facility to steam clean, but it will not normally do any better a job than cold and will just cost you more in fuel.
Hope this helps.
Andy