The problem is that treating the incorrect simplification as good can be very tempting for teachers.

For example, in an introductory physics course teaching Newtonian dynamics without the brutal complications of special relativity and general relativity is fine because it doesn't take much to explain that it is an approximation and it is good enough for "everyday" situations. Students are aware that a better model is available: worst case, they try to get away with not using it.

On the other hand in an introductory programming course teaching that if you have Animals in the program the dog instances "should" belong to a Dog subtype is logically consistent and elegant; the only opposing force is the abstract and uncool engineering principle of keeping software simple, and many teachers are dogmatic and enthusiastic.