I would say the vast majority of their retention problems had more to do with their crap legacy network than handset pricing.
Sure you're not saving $100 on the handset that a new customer would, but what are your other options?
A. Leave Sprint, pay the exact same amount for the same handset and switch to another carrier that more than likely costs more,
B. Stay with sprint, pay the same price you would for a handset at another carrier, and pay less monthly.
The people that would likely choose option A generally would have another underlying issue and would likely churn anyway.