LGPL requires that any distribution be able to replace the LGPL component with a modified version. If you use it as a shared library (er, DLL in this case I guess) you get that for free. But if, for example, you want to link a LGPL library statically you need to provide a static library containing the rest of your program in a linkable form.
The point is to allow the user the ability to exercise their right to modify the LGPL library and use it. The license you describe would presumably allow Microsoft to ship a binary with a fixed and unchangable libgit2 implementation.
For what it's worth, our analysis is that the ability to replace the libgit2 DLL is a requirement. (Not being a lawyer, however, I don't really remember the rationale here.) So, of course, we ship the source we used to build the DLL and you're welcome to replace it.
The point is to allow the user the ability to exercise their right to modify the LGPL library and use it. The license you describe would presumably allow Microsoft to ship a binary with a fixed and unchangable libgit2 implementation.