Fringe Nuptials

According to the Los Angeles Times Anna Torv, aka Fringe's Agent Dunham, has married Mark Valley, aka Fringe's mostly dead Agent Scott. I guess they tied the knot in secret over the recent holidays, and I don't mean Ground Hog Day, and only now have revealed their union.
Good on them and I wish them all the best! Typical of most real life pairings, I just didn't see their chemistry on screen. Isn't it odd that off screen couples seldom look hot together on film? I'm chuckling to myself just idly recalling how disastrous Tom Cruise and Nicole Kidman were in 'Eyes Wide Shut'. Wooden, but not in a porn-y sense, leaps to mind.
But why is that noncouples have the best onscreen chemistry? Take Booth and Brennan on 'Bones'. What Emily Deschanel and David Boreanaz bring to those two characters is really electrifying. It feel so real, but of course it's just fake. Maybe the reason that real couples can't project their chemistry is because they're trying to act and you can't bring something that's already there...And before I get more convoluted, I'll go to the post office.