Why bother with even parity?
A single parity bit can only check for the presense of single or odd numbers of bits in errors so expecting it to detect when a peripheral is disconnected is probably expecting too much. 

However, many systems will produce a continuous series of 1's when a peripheral is not present and this can be achieved with a simple pull-up resistor on the returning data line. If there was actual 8 bit data being returned by a connected peripheral then the parity bit would be zero for decimal 255 being transmitted. So even parity can detect when a peripheral is disconnected under these circumstances.

If odd parity were used, 8 high bits (decimal 255) would result in a high parity bit so rendering odd parity useless as a means of detecting loss of peripheral chip.

Horses for courses.