Yeah - I'm pretty sure "box" is a British idiom. See also "the idiot box" or indeed "gogglebox."
As an aside - Strictly Come Dancing was always going to have to change its name to what became Dancing with the Stars because of its contrived title that reference both the Baz Luhrmann film and a mainstay of British TV on the 70s and 80s, Come Dancing, which was a competitive dancing show that aired on BBC1.
It was always "series" rather than "season" in the UK. I assume the primary reason was that our "series" didn't run all year around. I know that's not really the case any longer, but then shows aren't "taped" either :-)
If you picked up a copy of The Radio Times (the BBC version of "TV Guide" - that mostly covers TV despite its title) you would always see "New Series" in italics above something new. And continuity announcers might well inform the audience during the credits of a series' final episode, that said "series" would return next year.
Adam