They do the medical just to check that the applicant will not be a burden to the Canadian healthcare system. Diabetes shouldn't be an issue as it can be treated with medication. Same would go for high blood pressure.
As Taj p and LM86 said, it's only to check for STDS, TB, AIDS/HIV, and anything else that could cause an epidemic like SARS, avian bird flu, measles, mumps, rubella, hepatitis, foot in mouth disease, swine flu... Which causes a lot of headaches for healthcare providers and pandemonium within communities.
But how did you get the medical results? As far as I know, they don't tell you the results but send it directly to CIC.
