If DLL's in C++ don't support binary encapsulation, when is it ever right to use them?

So I'm reading up on COM's and DLL's, and it seems as though, that if I'm ever to update the implementation of the DLL (if the needed memory exceeds the old need), I need to recompile the program using the DLL with the updated DLL. So I'm just wondering, when is it ever right to use DLL's in favor of COM? It seems nearly impossible to get all the programs recompiled, just because a dependency they have updated.

Also, just a quick side-question: Why is binary encapsulation not a problem in .NET? How come I can change a DLL just find in .NET without having to recompile my old project, without using pimpl/opaque pointers and whatnot?