As everyone has stated, there is no requirement for flushing your injectors. In fact, some manufacturers even have service bulletins indicating that some flushes may do more harm than good.
The only time a flush (injection, transmission or cooling system) may do any good, is if there is a problem that indicates it is needed. The rest of the time, it is a waste of money.
As was stated, most of today's fuels are such that the additives in them don't warrant any fuel system cleaning other than scheduled fuel filter replacement.
If it is a dealer saying that it is a required service, challenge them. Tell them to show you in the owner's manual where it specifically states it is required, or for that matter, even recommended.