Why does Blender warp UV pelt when unwrapping tight geometry? Often when I am modeling something I need to add some very fine detail to certain areas of the mesh so I add some very tight loop cuts in that area.  However when I go to unwrap it, even if it is very simple square geometry Blender will severely warp the pelt. 

For example, if I have a simple cube and unwrap it it looks fine:


But if I add a few very close loop cuts the pelt is horribly distorted:


Here is another example:


In both these cases the geometry is very simple and box-like, all quads.  But it becomes distorted when I unwrap it and I have to waste time manually aligning all the edges in the UV editor.  This also sometimes happens when I have many proximity cuts for use with a subsurf modifier.

Why does Blender do this and is there a way of preventing/fixing it?
As mentioned in the comments, Blender supports two algorithms for making a 2d projection of the mesh, Angle Based and Conformal. Angle based is the default and generally handle complex and organic shapes better, but runs into problems for some cases (e.g. the tight loop cuts you are using). In these cases it is best to try the Conformal algorithm.

The conformal term comes from the mathematical term conformal map, a function/projection that aims to minimise the difference in angles between the source and destination.
More details on the particular method used can be found here if you are mathematically inclined.