Yeah there's probably no effective difference here, this was added to be strictly compatible with the type specified in the spec WebIDL for the corresponding field.  There are a couple of places in the API I changed what would more correctly be a UInt32 to Int32 for less burdensome code (e.g., TypedArray index types) since C# code is generally more int-based, I didn't in this case because the type largely stays confined in the enum.