@Grantapus I'd say because it is not customizable hardware wise. It's like overclocking an OEM PC with a stock cooler. And it's possible that the CPU is underclocked because its silicon isn't good enough for 1.7ghz so they used it in this model and saved the more stable CPUs for higher end models.
Okay, I read into it a little.
I found out that devices with the 600 are indeed clocked at 1.7 GHz .
The reason that Asus wanted a better CPU, but google wanted power savings.
So in other words, this device was designed to run at 1.7 but google wanted it to power save, so it ended up only being 1.5
BTW, 95% of the time I have my nexus on power save, limiting the CPU to 1.2 GHz.
And when the CPU is running at 1.7 - 1.8, the tablet is only 2 degrees higher than 1.5