The Flash achieves this success margin through the NXP proprietary Memory Accelerator Module (MAM). The normal Flash access time is approximately 50 ns, so execution out of Flash even with zero wait is 20 MHz maximum.  In order to execute at 72 MHz, NXP developed and implemented the MAM instead of a cache due to the deterministic nature of the MAM.  With a cache, a user cannot always predict how long an instruction will take to execute, whereas MAM is deterministic and repeatable. The MAM also has an enable/disable feature and different programmable modes.