These are the most common among VHS casetypes. They were there at the dawn of VHS, and there until its death. Why were these most common? Because they were efficiant, in that they were the same size as the actual VHS and that they were cheaper to manufacture. When the VHS was still a relatively new novelty, they were released in a slipcase that surrounded the entire tape. A flap would have to be unfolded from the side or the bottom to slip out the VHS. These would last until the mid-80's, when the novelty or privledge of having or renting VHS's died. As they became more commonplace, distributor's realized that just a slipcase would suffice (unless they're trying to market a video in the video rental industry with big boxes).
Note: At first, I couldn't decide where to place the early Columbia Pictures Home Video releases, since they opened in a similar fashion as the book boxes. I eventually decided to place those Columbia boxes in the slipcase catagory because they're essentially the same structure, just with an extra flap. They're out of the norm for slipcases, but still a slipcase.

Types of slipcases: