When you reach their size, it's not a big deal to build and maintain your own DNS serving infrastructure; in that case, you can do as you please, which might in

When you reach their size, it's not a big deal to build and maintain your own DNS serving infrastructure; in that case, you can do as you please, which might include serving up a pool of A records round-robin style or using an expensive magic DNS geodirector thingamabob.