It's very basic, so basic it lacks all logic and every part of it is wrong.
Being ahead if he goes slow he'd force Hamilton to pass him(chance for contact) or back him up into cars behind. No chance is 100% incorrect and it's very obvious it's incorrect. If Hamilton has a bad pitstop, loses time, if he spins, he loses time, losing time from behind Rosberg is better than losing time from 5-10 seconds ahead of Rosberg.
It's plainly obvious that being ahead of Hamilton is both better for Rosberg and absolutely gives him a chance to hurt Hamilton.
Even having Hamilton in his dirty air can cause his tires to go off first, could cause his engine to overheat, could cause a failure.
Rosberg effectively has to win and hope for any mistake from Hamilton, he let Hamilton go into the lower pressure pulling away using his pace without being held up? Hamilton is now building up a large gap over 3rd which gives him more room for a mistake and for it to not effect him. He could be holding Hamilton up by a second a lap like at brazil or as is, letting him build a half second a lap lead over 3rd.... he now has time to spin, be back on track in second and ahead of Massa.