Blood pressure during exercise
As pointed out in the answers above, your blood pressure increases transiently as you exercise because more oxygen and nutrients are consumed by your muscles. However, regular exercise increases your "cardiovascular reserve"-this means your body will be able to function well at lower blood pressures. However, caution must be taken in hypertensive patients whose blood pressures are already up the roof. In these patients, gentle exercise and life style modifications (diet, stopping smoking, weight loss etc) may reduce their blood pressures over time. This will also reduce their risk of cardiovascular catastrophes in the future.

So whilst exercise will reduce blood pressure, it is not recommended as a first line of life style modification in hypertensive patients because exercise itself is stressful initially and stress is also bad for a hypertensive patient. Hence, exercise is good but gentle exercise is recommended for hypertensive patients. But again I doubt gentle exercise will do maximum good to your cardiovascular system because the type of exercise that helps lower your blood pressure is one that makes you sweat (e.g tread mill, etc). But once the blood pressure of a hypertensive patient is under control, then they can safely exercise and this should help lower their blood pressure long term. I hope this makes sense.