If Flaps 30 is used on a 737-800, that setting is more likely used because the aircraft flies like a drunken pig on ice skates at Flaps 40 with any cross/tailwind.
Maybe it's just me, but I've found I've had more control hitting a landing spot with Flaps 30 in wind than suddenly wallowing at less than 300' with Flaps 40. Cue in the tailstrike risk in that situation also.
That being said, I try to maintain currency with Flaps 40 and the crappy handling characteristics of the B737-8.
The recent discussion of idle power approach and landings as it pertains to AA is ridiculous. Same for the use of reverse thrust.