FT232R chip and capacitor
"Given that USB is DC isn't it just a break in the circuit?" USB has 5 V DC on pin 1 and ground on pin 4, that IS DC. The signal (AC) is on pins 2 and 3. The 10 nF capacitor is for DC decoupling, it has nothing to do with the USB data signal. 

Decoupling the data signals like that would not be a good idea, the data would not be able to get through.

Sure probably you could leave it out and thing might still work. But it is good practice to decouple, it can prevent problems that are difficult to diagnose.

No these capacitors are not only for EMI suppression, all CMOS circuits (and 99 % of ICs are these days) need decoupling on their supplies. When a CMOS gate switches it very briefly draws a current peak. If there was no decoupling, the supply could drop resulting in unexpected behaviour, the pulse might need to follow a long path causing RF signals to be transmitted.

In this particular circuit indeed, nothing is done with the data lines from the FT232 but this circuit is just an example, normally a serial interface or SPI bus would be connected to these signals.