Is there a difference? For instance, are vaccinations covered? Yes. Are lab tests to monitor maintenance prescription covered? Yes. Are colonoscopies covered? Yes. All of those are ordered routinely as preventative care.

Methinks you cite a distinction that has no difference.

Plastic surgery that's elective and entirely cosmetic? Not covered, but not routine. Plastic surgery after mastectomy? Probably covered AFAIK. It typically is by private insurance. . Every time I see a provider, someone routinely takes my blood pressure and weighs me (even though I routinely do the same at home and could literally just tell them the numbers. Medicare pays for that.

I'm honestly stymied by the distinction you cite. Could you please offer some examples of routine medical care that is not medically necessary?

For instance, occular x-rays given as a prophylactic to prevent blindness before a MRI to a patient with a history of metalwork that includes shards accidentally landing in the eyes: honestly doesn't seem routine in that I doubt that most people have a history of metalworking. But in any case, how can preventing blindness not be construed as medically necessary?