SQL Timestamps

I was just reading a work around for timestamps with LINQ or WCF, and I must be stupid, but I just don’t get it. In fact, ever since dotnet came out mapping timestamp to a byte array or SqlBinary, I never got why they did that.  Timestamp is 8 bytes, so why not just map it to Int64 or UInt64 and for nullable timestamp columns map it to Int64? or UInt64?

Is there some reason why .NET maps it to a SQLBinary type even though we know it’s a fixed size not a variable size ?