I bet it is, 400g is 53.47 CUBIC FEET of space. It seems the 40/55 gallon tanks are very popular with the pet stores to sell with bp's (and any other snake) need it or not.
I was actually asked to leave when I told a guy that he didn't need a 55g, with 4 heat lamps. 4 logs and a TON of other things to make his baby happy. I said "just get him a shoe box 2 hides, a thermomstat, a hygormomiter, some flex watt and a water dish and you will have a happy snake. It cost a LOT less than that....... equipment.