The Canon EF 50 f/1.8 is indeed from ancient times, it is a pre-historic lens.
It has paid for itself a long time ago.
The Pentax new 50 f/1.8 is a new construction, new optical design, and Pentax wants to get their development money back. Plus the optical design is likely to be very good, if we judge from the new 35 f/2.4. Optical quality like the Limiteds but in a plastic body.
I believe that the problem is that people just compare focal lengths, aperture and price - and not optical quality. Do you want a 50 just because it is cheap, or do you want one because it is good? If you want a cheap 50 then you have this in the 18-55 kit zoom...