Different countries have different copyright legislation but there are many similarities in the way copyright works here in Australia and the US and UK. The underlying principles are the same. Copyright, along with things like patents and trademark protection (which applies to Disney characters) forms part of a range of legislative protections designed to protect Intellectual Property (IP). The thing to remember with copyright is that it does not protect an idea, only the way the idea has been expressed. So, whilst copyright may exist on, for example a ballistic helmet or item of uniform, it means that those items may not be reproduced (i.e. copied) without the appropriate license or permission. Creating a model figure is not making a helmet that is a copy of the other helmet, so the copyright protections do not apply. The model figure is the expression of an idea for a model that is in a certain pose, wearing a certain uniform and carrying specific items of equipment. It is a miniature model, not a helmet etc.
Now the thing to remember is that once the idea has been expressed in the form of that model, it IS subject to copyright protection. The key phrase to remember is that copyright does not protect an idea (that's one of the reasons patent laws exist), only the EXPRESSION OF THE IDEA. So, if K&C produced a figure that I liked, I could not buy one, create a mold and cast my own because then I am reproducing K&C's expression of an idea (the model figure in a specific pose wearing specific clothing, equipment etc) and would therefore be infringing on K&C's copyright.
Trademark protection as used by Warner Bros, Disney etc for the protection of their characters is a different form of IP protection to copyright but is often used in conjunction with copyright to restrict abuse of the owners Intellectual Property.
Hope that clarifies things a little,
Jules