If that's what you call it, but business have had their paid Google Apps accounts nuked, and critical data lost. Publishing on Play is basically mandatory to get users.
Being on Play is an enormous advantage, there's no question. Whether or not it's mandatory probably depends on what sort of app it is, though.
There are successful apps that aren't in the Play store. But being successful without being in the Play store requires a larger marketing effort.
If that's what you call it, but business have had their paid Google Apps accounts nuked, and critical data lost. Publishing on Play is basically mandatory to get users.