Aren’t Expression Blend 4 for Windows Phone and Expression Blend 4 the same product?
No. Expression Blend 4 enables authoring for Silverlight 3, Silverlight 4, .NET 3.5, .NET 4 and SketchFlow projects by default, installing Expression Blend 4 for Windows Phone will add phone authoring capabilities to your existing Expression Blend 4 install. Installing Expression Blend 4 for Windows Phone independently without a previous install of Expression Blend 4 will allow the creation and editing of Windows Phone projects only.