You only have to look at some of the Demo Scene stuff to see that you can get some amazing city-scapes with average processing power, and DB knows his Assembly onions too so...
here's hoping!
I have played with Fractals a bit, and the concepts' adaptation is beyond my skills, but considering the server load and the ability of the persons' setup to make these calculations can vary greatly, from model to model and format to format etc.
Laptops are especially prone to outdated hardware\software configurations, for example with usually no recourse to upgrade components.
I think whatever type of procedural generation FD are planning for their cities would be more random and thus natural to human design than fractal design where patterns are clearly visible.
It's pretty clear that FDEV need to hide some of the issues in a clever way, huge cities that we can explore are really not needed, however the illusion that you are visiting a MEGA City certainly is.