"but the publisher insisted that we had signed a contract, and that with-or-without assets we were expected to deliver the alpha version on time....which at this point was a week later."

Crazy, yet all too common. We didn't hold up our end of an agreement, but YOU have to. Does this happen in all industries, or just software?

"We didn't provide the plants or mulch or dirt for the garden (which we were supposed to do last week), but you still have to provide a flower bed tomorrow."

I'm assuming there was something in the contract that the original party was required to provide assets for the port. Perhaps it wasn't.

"No... no need to contractually obligate us to deliver - just believe us, we'll get you the files!"