Not true I'm afraid.
The launch partners I've asked (granted, just over Twitter), all have the £20 limit.
That's McDs, BP, Morrisons, KFC, Costa, and one or two more I can't remember. All replies to say it's a £20 limit.
Odd, so that makes all retailers that have Contactless terminals effectively launch partners.
Sounds like the only point of being an official launch partner was for free publicity.