Do cats meow only to humans?

[UEL]

The other day on the drive to work, the morning crew at the radio station had their usual "fun trivia". Most of their items are typically of no consequence, quite humourous in their oddness, and purely entertaining. Thursday's was one such one. It was on pets.

Their one claim that got me thinking was:

Cats only meow with humans. With all other creatures, including other cats, they use other forms of communication.

Now, I've been to Rome and the Colliseum. I've heard the noise of the feral cats there. I'm pretty sure that they weren't all meowing to me. So, I'm a bit leery of this claim.

Do any cat lovers have any ideas?