Arch Linux is a rolling release, which means performing an update leads always to the newest version of Arch Linux no matter with which version you started.
But there are is a reasons why you might want to use the newest image:
The new image uses ext4 instead of ext3. Personally the first thing I did with my SD-Card was to change file format to ext4. ext4 is faster than ext3, has more features than ext3 and personally I consider it to be more stable than ext3.
This should be it from now on. As maribu said, changed rootfs to ext4, there were kernel problems that might have prevented updates, and update problems where the 2 config files might disappear.
Looks like midori package is broken, btw, might be something to do with libwebkit