Eventually, a few years from now, they'll have a better understanding of the full stack, but for now, we want to clear as many possible roadblocks from their way so that they don't either abandon web development or begin using Programming languages which are reasonably Hospitable to People who come from non-traditional backgrounds.
Also "relatively clean system" is an important qualifier. A lot of curious developers won't have one of those, and instead will have to deal with dependency hell and tedious gotchas.
Jumping into learning about the framework is better use of their time upfront.
Also, this is a weird conversation to be having with a dude who has a book for teaching beginners Ruby (http://ruby.bastardsbook.com/ )!
No seriously, though...So many things can easily go wrong with basic Rails...not because Rails is bad, but because Rails has so many features...that if people haven't mastered the art of Googling lines from debug-output or command-line install instructions...then the time they've "saved" by having a push-button solution will be more than spent in the time trying to get off the ground.
But I'm obviously speaking from hindsight...as I've gotten more experienced, I've seen that writing script for minimal apps is more efficient than launching a full-fledged Rails app. However, I may have lost interest in the whole web-app game long ago if I didn't have the chance to play around (clumsily) with Rails 2.2
which is why i had stage file with gentoo prefix instead of all the other stuff, while i was still fulltime osx
http://reza.jelveh.me/2009/05/20/gentoo-on-os-x
i'd be surprised if that stage still works though.