As far as I've been able to see from my limited testing, Pages also cannot 1) comment on Profile's posts unless they have been Circled by that user first (and maybe mentioned, though I don't think too many people have had a way to test this yet).
2) Cannot +1 under the same circumstances, because a +1 is sort of like a micro-comment? Not totally consistent, because you can at least Share.
3) You can do everything as normal among Pages, i.e. Circle them as a Page, comment, and +1.
Also: Typing '+1' just now, it began to auto-fill the names of about a gazillion Pages that have their newly minted names start with '+1. something', like a lot of soccer clubs in Germany, e.g. "1. FC Koeln", asf. Wild.