That's the Key!

I find that when I get a song/piece stuck in my head, there is a far greater chance that I will be humming/singing/thinking of it in precisely the right key if it's a pop song than if it is classical music (say 19th century and earlier).

Does that make any sense?

Now I know this because often if I have an Ohrwurm (German word for "a song stuck in your head; lit.- "Earworm") and I have access to my computer, I will play it aloud on there instead. Since I always do this while the song is still playing in my head, I know the relative relationship between the key in my head and the real key of the song as it jumps from my brain to the speakers, so to speak.

If any of you have never really studied music theory and have no idea what I'm talking about, I'm sorry, it will all be okay, and I'll try to write more coherent posts otherwise.

At any rate, this usually happens infrequently with classical pieces, despite that I have ChopinSchumannBeethovenBachMozartTchaikovskySchubertDebusseyetc. in my head all the time, at some point in most every day. Yet I've been right on with pop songs enough times to be noticeable for me. It's very strange to me... I would love to know exactly why...