I agree with the principles behind responsive web design, but I think this is a good thing to keep in mind when talking to clients:

Timing is everything. For businesses that are trying to turn a profit, their return on investment (ROI) matters. Although mobile is important, it still amounts to a very small percentage of the overall traffic for many organizations. So, quite often, optimization for mobile lands at the bottom of the design debt list […]. Business considerations, particular features and technical issues in the shop often have a higher priority, especially if the client’s company is relatively small.

— Giving Our Clients The Best Deal In Mobile by Paul Boag