I obviously do not have the answers as to what the difference means but IMO the most plausable explanation is that the "agreements" are a royalty situation and the "purchases" are one time buy outs. Note the "agreements" come with expressed confidentiality and the "purchases" do not:

RIMM:

"...have agreed to the terms of a patent license"

"Terms of the deal are not publicly available."

J2.5:

" The terms of the settlement included the grant ...of rights ... in the form of license agreements"

"The parties have agreed that the details of the settlement are confidential."

ONKYO and every other company:

"...has purchased a ... license"

No expressed confidentiality

The Rimm language is exactly what I would expect to see in a royalty situation - "the terms of a patent license" - they have not purchased and therefore do not own a license, but they get to use pursuant to the terms of a license as long as royalties are being paid. Same with J2.5, "in the form of" a license sounds the same as according to the terms of a license with the implication that it is conditioned on royalties being paid. Of course there could be more to it but it seems to fit pretty neatly. As others have pointed out, we should not be forced to have to speculate as to the meaning of the language used in the PRs but we dont have much of a choice.