From the mkfs.ext3 man page: -b block-size Specify the size of blocks in bytes. Valid block-size values are 1024, 2048 and 4096 bytes per block. If omitted,

From the mkfs.ext3 man page: -b block-size Specify the size of blocks in bytes. Valid block-size values are 1024, 2048 and 4096 bytes per block. If omitted, block-size is heuristically determined by the filesystem size and the expected usage of the filesystem (see the -T option). I remember that Red Hat and Fedora used 1024 on my computer. As for the distribution specific thing, maybe some distribution had their own version of /etc/mke2fs.conf (settings for mkfs, including block size).