We've often blogged about Section 508 compliance as a means to convince very engineering-centric developers to consider their users.
Accessible designs work for everyone - see also Universal Design. Ever use a curb-cut?
By thinking about a disabled user and designing a solution that works for them, developers adopt a user-centered design strategy without even knowing it.
It is an excellent foot-in-the-door for designing for an admin user, a casual user, the sales team, an expert user, and many of other personas associated with the solution.