What LW&B said.
You can get away, as amateurs on fun rides, where one of you 'carries' the other for some of it (I have better stamina than Mr Smith, I'm almost always pushing harder at the end). Both being on top form for the whole ride is nigh on impossible. And when you're both struggling your team performance is worse than one rider flagging on a solo.
They took a big chunk off the previous record. Awesome.