I guess it completely depends on the need of the business. If the company thinks that the developers can do enough of the DBA side of things (backups\indexing\query plans\performance monitoring\auditing plus loads more) then your probably ok with developers.

When it starts getting to a point when developers are spending most of their day doing admin tasks then its probably time to get a DBA, unless of course management are happy for the developer to not be developing.

In my experiance developers set things up and then leave them, possibly running the odd reindex job etc. I know this is a complete generalisation and many developers will also be awesome admins, but some are just developers.

Like i said at the start, it depends on the business.