Odd - I just checked it using my system, and it works fine:
USE [Testing]
GO
SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
CREATE TABLE [dbo].[Users](
[id] [int] IDENTITY(1,1) NOT NULL,
[Email] [nvarchar](max) NOT NULL,
[dt] [datetime] NOT NULL
) ON [PRIMARY]
GO
ALTER TABLE [dbo].[Users] ADD CONSTRAINT [DF_User_dt] DEFAULT (getdate()) FOR [dt]
GO
id Email dt
1 MyUser 2015-02-12 17:27:48.127
So what am I doing that differs from you?