1) This is a preliminary injunction, not a decision. An injunction which resets a situation to the former status quo pending a decision isn't all that unusual.
2) I don't think the issue here is so much a "warranty" as much as that Automattic (et al) set out to discriminate against WPEngine to obtain a business advantage. If Automattic wanted to shut down the WordPress plugin repository entirely, they'd be within their rights to do so. (It'd be business suicide, of course - but the point is that they could.)