I'd like to go a step further on this topic and mention that in May 2006, TRAINS Magazine published an article titled, "The Young Guns of Steam." This elicited several pages of comments on RyPN the next month - well worth reading.
I posit that the interest in steam comes from two sources. To the elders, it represents the "good old days," (1950s) when schools taught us to "duck and cover" in anticipation of Soviet nuclear attack, polio could imprison us in an iron lung, and blacks and homosexuals knew their places (back of the bus and under the bus respectively). For people of all ages, the second source applies: Steam engines are exciting to watch. They are big, noisy, smelly, and the ground shakes as they pass. There are all sorts of rotating, sliding, and thrashing motions going on. They are living beings, and watching / hearing / smelling / feeling their passage is a mufti-sensual experience. Best of all (or worst of all), they require lots of care and attention, thus providing excellent volunteer opportunities at all skill levels.
-John