Who cares about Domain Rules?

namespace BusinessRules.Evolution_Two
{
    /// <summary>
    /// Investor Domain object that is abstract to form the base 
    /// for all other specific investor domain objects.
    /// </summary>
    public abstract class Investor : IInvestor
    {
        #region Fields

        private double income;

        #endregion

        #region C'tors

        /// <summary>
        /// Initializes a new instance of the <see cref="Investor"/> class.
        /// </summary>
        /// <param name="income">The income.</param>
        protected Investor(double income)
        {
            this.income = income;
        }

        #endregion

        #region Factory Method

        /// <summary>
        /// Creates a new investor infered from the culture info.
        /// </summary>
        /// <param name="income">The investors income.</param>
        /// <returns>Returns a specific investor for the current culture.</returns>
        public static Investor CreateInvestor(double income)
        {
            ICurrentCultureInfo cultureInfo = new CurrentCultureInfo();
            return CreateInvestor(cultureInfo, income);
        }

        /// <summary>
        /// Creates a new investor infered from the culture info.
        /// </summary>
        /// <param name="cultureInfo">An instance of the current culture info.</param>
        /// <param name="income">The investors income.</param>
        /// <returns>Returns a specific income tax engine domain object.</returns>
        public static Investor CreateInvestor(ICurrentCultureInfo cultureInfo, double income)
        {
            switch (cultureInfo.CurrentCultureName)
            {
                case "en-NZ":
                    return new NewZealandInvestor(income);
                case "en-AU":
                    return new AustralianInvestor(income);
                case "en-US":
                    return new USAInvestor(income);
                default:
                    return new NullInvestor(income);
            }
        }

        #endregion

        #region Properties

        /// <summary>
        /// Gets or sets the income.
        /// </summary>
        /// <value>The income.</value>
        public double Income
        {
            get { return income; }
            set { income = value; }
        }

        /// <summary>
        /// Gets the tax liability.
        /// </summary>
        /// <value>The tax liability.</value>
        public abstract double TaxLiability { get; }

        /// <summary>
        /// Gets the tax rate.
        /// </summary>
        /// <value>The tax rate.</value>
        public abstract double TaxRate { get; }

        #endregion
    }
}