Why are hardware inverters so prevalent?
There are a few factors here.


Single stage circuits are nearly always inverting. This comes from the fundamental behaviour of the transistors. 
The polarity of the input doesn't just affect the interpretation of data bits, it also affects the interpretation of start and stop conditions.
Serial receivers are generally implemented in hardware. 


Point 1 explains why we end up with inversion in the first place. An inverting line driver or line receiver is simpler than a non-inverting one.

Points 2 and 3 explain why if inversion is needed it must be implemented in hardware. On more modern hardware where logic is cheap and Pins are expensive there may be a programmable inverter inside the chip but not everyone seems to have realised this is a good idea yet, so there are many products out there with fixed polarity.