Is it that one misses social cues or that the other lacks effective communication skills?

It seems like an either/or situation on the surface of it but I'm inclined actually to say that lots of people just don't pick up on social cues. It's a subtle thing. I'm hyper vigilant, especially socially and pick up on hints and cues even when people aren't good at communicating.

Yes to both.

See if I didn't express myself effectively then why would I expect someone to understand me.

One wants to force the other side to be direct. So one fakes both.