The old Azalea vs. Rhododendron debate

Hello, Tamsin! I’m in here this morning catching up on my backlog of e-mail and g-mail and blog work, and I saw your fascinating piece on our azaleas and rhododendrons. This will be very helpful to all of us in talking with customers, but I have an even simpler (and yet devilishly difficult) question for you:

What do you say when customers ask the difference between azaleas and rhododendrons?

I know the horticulture, but they don’t really want to hear that — they want to know which one they should grow, and how they’re different. Do you have a simple answer to that? I always go into the "all azaleas are rhododendrons but not all rhododendrons are azaleas" bit, followed by a brief something about interbreeding. But it always seems feeble. Got a down-and-dirty response that gets the message across?