Rev limiters on ecu's are achieved by cutting fuel or cutting BOTH fuel and ignitiion.
This is done to prevent unburnt fuel getting into the exhaust. The unburnt fuel would ignite the moment fuel and ignition are activated again when the rpm's drop, causing explosions, excessive heat and large flames in the exhaust. Imagine what this would do to a catalyst.

A rev limiter also works in cooperation with the boost control software. The ecu will lower the boost just before hitting the rev limiter. So, you are never at full boost when the rev limiter kicks in with a standard ecu. Don't know what all tuners (professional and otherwise) have done with these settings.