The ease with which an exploit can be fashioned is largely dependant on the level of access given the attack vector and the complexity of the code governing that vector. From Autoplay to VNC, the more control given the remote source, the more potential for manipulation.
As we demand more from web applications and the technologies that enable them, we will open avenues of exploitation, almost by definition. New demands on developers, engineers and designers will be a natural result of this.
On the bright side, this likely means a richer employment environment for web professionals; the flip side is it probably means more jobs for web hacks, too.