"Rather than bore you with a lot of details about vapor pressure and boiling points, lets just say that you can get plenty of steam with out the water actually being at a boil."
Yes, you can, but that doesn't really have anything to do with making a cup of expresso.
The roast, type of beans selected, and the amount of time the steam and water are in contact (VERY short compared to regular coffee) with the grounds are far more important to the process of making expresso.
Were you to try to make regular coffee with expresso beans/grind, you'd get a very, very rude surprise.