There are plenty of situations where Petco can make out like a bandit by buying Dr.F&S, physically close the ware house, even the livestock center and still profit.
The most obvious, is that they can keep the online present and just ship things from the very large Petco Warehouse which they already have. They just cut a huge cost and, if they careful and provide the customer service as before, they will retain all the customer base.
It is unlikely that they can do the same with DD, I don't know, but LA will go the same way in the future IMO (baseless opinion).
Like I said, we have no information. I think it is funny that some of us seem to give his uninformed opinion as a sure thing.