'On us' should mean free, right?

Too MPSIMS-y for IMHO, really.

My Roku box is advertising The Good Dinosaur. “WATCH NOW, ON US” with the Google Play Movies and TV logo underneath.

When I follow the ad, it takes me to Google Play, where I can rent or buy the movie, for money.

All of the other similar ads for paid-for movies just say ‘Watch now on Google Play’

Semantically, I guess ‘US’ could be argued to mean ‘Google Play’, but ‘on us’ (falsely) implies free of charge, right?

I agree with you.

I think they intended to give you something for free and it just didn’t work right. I’ve had those offers and watched free movies on Roku channels.

You can watch it on Google or on another service. Which one do you want to watch it on? Us or them?

Seems like false advertising, to me

I thought it meant “Our fault (sorry about that, we’ll take the blame)”.

Which reminds me of one of my favorites:
You get a spam email from some company with a typo in the subject. A couple of hours later you get another email apologizing for the typo, but we’ll make it up by allowing you to buy something you don’t need for a small discount.