Hate to burst your bubble, but 4.0 came out over a month before Cataclysm did. With 4.0 hunters did have focus in Wrath of the Lich King and MM hunters used Arcane Shot as the focus dump. This was the case until after Cata hit and SV with Cobra Shot made MM look like Wrath Subtlety Rogues. So, yes, MM did use Arcane as a focus dump from 4.0 release until Cata release at which point no one that cared about doing reasonable damage stuck with MM.
Back on topic, BM will continue to be a horrible spec to play on most fights in Tier 11 specifically because of target switching, adds, or bosses that can't be hit with a pet during certain parts of the encounter. BM still has the worst AoE and a target switch means you lose pet dps until it reaches the other target. BM would still be a situational spec at best. Although, at this point it looks like they're making all 3 specs into situational specs which is starting to make me feel like I'm playing my druid again. Dual spec isn't enough...