Chris Mason changed the default meta-data block size on Friday with this Git commit. The meta-data block size was changed to 16KB by default (or the page-size if it happens to be bigger than 16KB) rather than just defaulting to the page size. Chris Mason's commit message explains that a 16KB meta-data block size for Btrfs yields faster performance and less meta-data fragmentation for almost all workloads. The downside to the change is a slight increase in lock contention on root nodes for some workloads, but that can be worked around.
This change obviously only affects the creation of new Btrfs file-systems, but for the other recent btrfs-progs changes, see Chris Mason's Btrfs-progs git repository.