Cattle are now given supplementary B12, because their modern-day feedlot diet is insufficient in that nutrient. So, yeah, eating meat for B12 makes no more sense than just supplementing directly with the B12, which is probably unnecessary for just about everyone, vegan or not. I may have posted this link before, but here's the best article I've read on B12. It does recommend supplementation, but also clearly explains why that's probably not needed:
The McDougall Newsletter - Vitamin B12 Deficiency, The Meat Eaters' Last Stand