You can keep surgical staples in your head for over two weeks, although most surgical staples are removed within 7 to 10 days. The duration really does depend on the type of wound the staples are keeping together.
The answer to this is pretty simple. Different types of wounds heal at differing rates, and likewise, different areas of the body tend to heal at differing rates too.
For example, the scalp area gets a lot more blood to it, and therefore it heals relatively quickly. In this instance, surgical staples are likely to be removed more quickly than those in other areas of the head.
Non-surgical staples in the head
Surgical staples are safe because they're inserted by a medical professional, and are completely sterile before being placed into the body. Non-surgical staples should not be inserted into the body as this could cause serious damage to the tissue and could lead to awful infections.
Here's an interesting video that makes me wince a little bit, but shows how easy it is to remove head staples: