Afaik the problem is that XFS trusts the hardware to do the right thing during a power loss aka stop inflight requests before the brownout turns you disks and their controllers into heavily biased random number generators. Lots of x86(-64) hardware lacks a proper power loss interrupt triggered early enough to stop the all I/O in time. The ext3 journaling hides that problem to some extend by journaling more than just the minimal metadata required.