Unallocated space at the end of HDDs

NTFS filesystems are allocated on disk in terms of "Clusters". That is, a NTFS filesystem will never have a partial cluster at the end. Clusters can be specified (by default or by the user) to have a number of different sizes. The smaller the clusters are, the closer to 100% partition space that can be used. That said, the amount of unallocated space shown is trivial. I wouldn't be at all surprised if no formatting/partitioning software writer would consider it worthwhile to avoid that unused space, but you're welcome to shop around.

Modern kernels tend to create partitions so that their boundaries be at positions where data blocks don't have to split during fetching operations. I am far from being a windows expert but I dare to state that if you did not want win to create like that, then the mentioned optimization algorithm led to this structure.