He’s hedging his bets. He was getting pounded by other pollsters when he was sowing D+3 to D+5 when they were going higher than the 2008 turnout so he’s played it safe.
From business perspective, it is always better to be wrong when all your competitors are wrong, than to be wrong when all your competitors are right. Rasumssen sees the competitive landscape and decides to call it similarly to everyone else, so that if they’re all wrong, he doesn’t get singled out.