@X2 bhi jee, you can buy a bike with low cuts in tire, so speed wont get effected on the street.
its not tires, its about the frame and posture, a hybrid will be lighter, just like aluminum is lighter than steel, by design a hyrbid is lighter than a mountain bike in majority of the cases. and hybrids provide more options in terms of seating posture, which is a good thing for casual and recreation bicyclists.
IMHO dual suspension is really way too gimicky for majority of people biking, especially if you are on paved paths or mixed trails i.e. dirt, gravel, etc..even many fairly hardcore mountain bikers prefer hardtails rather than dual suspension because there is an element of control that changes, or rather control experience that is altered with a dual suspension bike.