Should psychological checks be as frequent as physical checks to evaluate a patient's condition? Are there differences between psychological and physical attributes that could justify the lack of these periodic tests in psychology?
ABSOLUTELY! The physical and mental are often connected. Take, for instance, the Thyriod. If the thyroid is physically unhealthy then it can cause mental disturbances. It can cause a slew of psychological manifestations for someone. When preceived by a psychological professional, they treat the symtoms they interpret and preceive from their paradigm they treat their patient with psychological techniques and medications. 

I have seen this first hand where someone can exhibit pyschological disturbances and are incorrectly diagnosed because the psychological professional does not test their physical state.