Heroku's free hosting is leaps and bounds beyond what a typical $5-$10 shared host offers, and there's an easy upgrade path. Sure, you can come up with specific usage levels where a shared host is cheaper on a bit-to-dollar basis, but you're still not accounting for Heroku's main selling point: convenience and saving developer time. This plus the fact that the vast majority of sites on $5-$10 shared hosting would fit easily on Heroku's free plan means that value-wise, Heroku faces much stiffer competition from Linode than any shared provider.
I like and am comfortable with both Python and Ruby, and one of the biggest reasons I choose Rails for projects nowadays is Heroku, and I'm not alone. Given this, I really don't see how you could claim Python has any edge when it comes to hosting. If you're concerned about what tons of shared hosting providers have installed, why not just use php?