GENIUS IS WHAT THAT WAS: On the one hand, Survivor-wise, yes. On the other hand, no.
Here's the thing: by voting out potential ally Matt, Rob takes his advantage from what could have been 7-4 (by voting out Steve) to instead 6-5, and now any member of his tribe (including the always unstable Philip) can flip over to turn things 6-5 the other way. Yes, Rob has the HII (and no one else knows), but I thought one of the things we knew about this game (as far back as Outback and Jerri's ouster) was that you're better to knock off some opponents first and save the self-cannibalizing for when it's safer.
True, at 7-4 there's the very gambit Matt suggested -- vote with Rob once, then flip and blindside -- but I think that if I'm Rob I'd rather use this vote to test Matt's loyalty rather than assume it's not there. But what do I know -- he's the one who's been on the show thrice before. Fun season.