They don't have to be, but in this case they are part of the 64-bit ARMv8 instruction set. ARMv8 also enables SIMD speedup. Look at the massive increase in score for AES and SHA:The 32-bit VIA C3/C7 was optimized for stuff like AES encryption. That sorta thing isn't necessarily due to a change to 64-bit processing.
http://www.anandtech.com/show/7335/the-iphone-5s-review/4