Just an update on this for anyone else who stumbles across this question.
Starting in .NET 4.5 you are able to compress a directory using System.IO.Compression into a zip file. You have to add System.IO.Compression.FileSystem as a reference as it is not referenced by default. Then you can write:
System.IO.Compression.ZipFile.CreateFromDirectory(dirPath, zipFile);
The only potential problem is that this assembly is not available for Windows Store Apps.