System.Numerics assembly missing in .NET 4 PCL

Hi,

I've just noticed that the DLL containing the BigInteger and Complex types (System.Numerics.dll or System.Runtime.Numerics.dll) is missing from Portable Class Library profiles targeting for .NET 4 (e.g. Profile5). The assembly is present in PCL profiles targeting (among other things) for .NET 4.5 (Profile23, Profile24, Profile46, Profile47, Profile7) or .NET 4.5.1. (Profile44).

Is there a reason why these types (BigInteger and Complex) are excluded from all PCL profiles for .NET 4? The types are introduced already in .NET 4 (according to documentation: http://msdn.microsoft.com/en-us/library/system.numerics.biginteger%28v=vs.100%29.aspx ), so why not allow PCLs for .NET 4 use these types?