Not long ago, I wrote about an article which found that people with psoriasis needed closer general medical monitoring due to higher likelyhood of several diseases.
This month's Archives of Dermatology has an article re-iterrating that indeed severe psoriasis does pose a risk to the general health of patients and may decrease life expectancy by several years (more so than hypertension).
The increased overall inflammation produced by psoriasis may be damaging the cardiovascular system in patients with severe disease. Notably, many drugs for psoriasis such as Enbrel are designed to reduce inflammation. Perhaps such drugs provide benefits beyond just treating the skin? Time will tell.