Earlier quoted context omitted.
I've been told academic journals don't even pay peer reviewers. Is that true? Peer review is the whole point of a journal and is what sets them apart from just publishing a PDF on the internet. If peer reviewers aren't even getting paid for their invaluable service, nothing stops them from forming their own independent peer review group.
In most cases yes, peer reviewers are not paid. These companies are pretty much a paywalled pdf hosting service hence the outrage against them.
The most I've personally gotten was a nice note from an editor; I've heard rumors of someone who reviewed enough to get some journal-branded swag (a mug or calendar, I think). If you review a book, you might get to keep the copy.
Nobody gets cash.