Why is the clock speed of the iPad Air 2 so much less than the Google Nexus 9

I was comparing different tablets and I saw that there was a big difference in clock speed between an iPad air 2 (1.4 GHz) and Android tablets like the Google Nexus 9 (2.3 Ghz). What is the reason for this big difference and what does it mean for the perfomance of the tablet. Does an android tablet just need a bigger clock speed to operate correctly?