The Concurrency Programming Guide says this:
You cannot create concurrent dispatch queues yourself. Instead, there are three global concurrent queues for your application to use.
Then the GCD Reference Guide says this:
dispatch_queue_create()In OS X v10.7 and later, specify
DISPATCH_QUEUE_SERIAL(orNULL) to create a serial queue or specifyDISPATCH_QUEUE_CONCURRENTto create a concurrent queue.
This is a bit confusing; it implies you can indeed create a concurrent queue yourself; is it a case of the docs not being updated to explain current features?
The docs you link to are saying that on iOS you can only create serial queues. On OSX you can create serial or concurrent queues.
This appears to be out of date since iOS5..
(Thanks to @omz and @Analog File)