The long and short of it is that Google has well documented instances of bribing/paying companies to not offer their apps on other stores, and Apple simply runs their walled-garden. Google deleted evidence of them doing this, which looks very shady. Also, the judge in the Apple case took an incredibly narrow view, something like "digital mobile gaming transactions". So Apple's 30% cut seemed to be in line with competitors.
Of course, I don't think either should be allowed to do this, but the legal argument against Google is stronger imo.