I think it's all explained here:
http://www.anandtech.com/show/6330/the-iphone-5-review/12
Essentially, at idle states, the cpu in the iPhone 5 draws far less power than the cpus on most smartphhones today, hence why we see better battery performance in tests that involves the cpu throttling down to idle quickly.
Under load however, it draws considerably more power than the average CPU so in tests that keep the CPU active and at max load, it'll drain quicker.
Hence, why the tests show the iPhone 5 doing very well in some tests, but being a total battery hog in others.
Hmm these tests were with web browsing, does the ip5 throttle down that much while actively web browsing? Interesting.