It's Free Software, you can run it yourself or switch providers at will. The catch may be in the lack of features compared to a proprietary option (like Heroku)

From their faq page: To get more information on the pricing and timing of a paid version of OpenShift please send an email to openshift@redhat.com

Yeah, is it free as in beer? For life? No matter how much it has to scale to?

If it is, I would like to understand the reasoning behind that? Is it to gain traction and visibility for Red Hate as a PaaS? And then...

It is in open beta and has big warning labels to not use in production.

The free tier is limited in resources; When you want more, you'll be expected to pay for more (once they begin to offer paid plans).