Long answer: Because it looks like a serial port to the PC application I can only assume they did what most people do, equate "serial" with "RS232", either because they didn't know any better (unlikely) or maybe as a marketing ploy because they knew most people make that connection.
I can't really think that either of those options is likely, after all anyone designing a board with these chips would know the difference and certainly those designing the chip would know.
So that brings me back to a marketing reason.
Short answer: No idea 
Rob