Like Mike said, I was talking about the key of D, not songs in D. The V ov V is a very common progression.

In theory class in college, we had to analyse scores this way. It's easier with the actual music because you can see what the melody is doing.

I didn't do a very clear job of explaning what I thought was going on. But if you think this is confusion, you should get into jazz substitutions some time.

That's when you really do need those stinking keys.