This is from the e2fsck manpage on my machine,

-a This option does the same thing as the -p option. It is provided for backwards compatibility only; it is suggested that people use -p option whenever possible.

Perhaps his version is newer and has dropped the -a support.

Edit: clearly I haven't been reading the thread at all.

"fsck -fay /" fails, because /etc/fstab still contains 'ext2' as the filesystem. However when you use "fsck -fay /dev/hda5" it won't look at the fstab, but use whatever filesystem it can derive from the superblock, i.e. ext3.