Why do suborbital planes feature H-tail and/or large wingtips?
Dreamchaser isn't intended to be suborbital. Don't know about your 3rd picture, but the Spaceship 1 &amp; 2 were designed by the same person/company, so it's not surprising they use the same design elements.  

The designs of Dreamchaser vs Spaceship N address two different problems.  An orbital vehicle has to decelerate from ~17,000 mph, while a suborbital vehicle on a ballistic trajectory (simplistically straight up and straight down) starts from zero speed at its high point, and needs to keep from gaining too much speed.  So if I'm not mistaken, a main function of the H-tail is to allow the entire vehicle to act as a drag device.  That wouldn't be practical for an orbital reentry vehicle due to heating &amp; aerodynamic forces.