Comment 16 for bug 1073433

To clarify as it is not completely apparent from the above discussion:
The repairs reported by fsck are not caused by corruption, but are harmless and purely cosmetic fixes. The reason is that to avoid performance bottlenecks, ext4 does not update the superblock after each inode or block (de)allocation. This is done on (clean) unmount instead and only to make it look good. The filesystem does not rely on this information.
The real bug is of course ubuntu not shutting down cleanly, and thus not performing the umount.

Then again if this is not an error in the fs, then maybe fsck shouldn't prevent the system from cleanly booting.

Theodore Ts'o take on it:
https://plus.google.com/117091380454742934025/posts/JmpczpdwgrQ