Regardless of other technical limitations I'm guessing that it's actually done on purpose, as point #3 in TFA states:

>Predictable – Googlebot can trust a page will render the same on each visit

It's probably important for Google's crawler to identify whether a page changed or not, if some elements in a page are randomly generated they may want to limit the impact.

I mean, after all they seem to use a real, changing value for their Date, so if they wanted they could just seed their RNG with that.