It sounds like odd. We are using this old technology in 2016. There was the communication card for Apple II in 1978 . RS-232, a standard for serial communication transformation of data was introduced in 1962.
The speed of serial port(UART: Universal asynchronous receiver/transmitter) is around a few hundreds Kbits to a few Mbits per second today. There are many fast serial communication devices out there, such as USB 3.0 which can theoretically transfer data at 480 Mbits per second.
But there are still some applications which do not necessarily require such a high speed, for example debug terminal and to control machine like CNC mill. Both HW and SW for serial port is simple, chip and easy to implement/debug.
Long time back (in 1998) I had engaged in a project where I designed and implemented a data link layer on top of UART. That was based on HDLC. I’d recommend to check out Eli Bendersky’s ‘Framing in serial communications’ for anyone wants to quickly catch the idea. Physical layer of UART communication has ability to detect error using parity check, which has limitation. We can add CRC at each frame to detect transmission error if we worry about it.
I got involved in design/implement a similar data link layer on top of UART interface between two embedded processors a year back. This old technology from the ancient is still alive!