There are reasons to prefer certain dailies over others. Only one of the Outland fishing dailies can drop the noncombat pets, and only one of the Northrend cooking dailies gives 2 awards. With this method, you can double up on these dailies, getting more of their specific reward.
Besides that, you could also want to skip certain dailies that are harder to complete. Perhaps you want to skip making Sewer Stew (4 Chilled meat) in hopes that the next daily is Infused Mushroom Meatloaf (2 Chilled meat). I don't know how the new fishing dailies will work in 3.1, but I'm sure similar arguments could be made for those as well.
So no, you're not doing one daily twice during the same lockout, but you're doing the same daily twice during the same "quest rotation".