Why does timespan totalmilliseconds have the same digits in the integer and decimal parts?

When calculating the millisecond difference between two DateTime objects I always seem to get a number returned where the decimal part of the number is the same as the integer component of the number. For example: 1235.1235

Why does this happen? Am I doing something wrong? Is this a quirk of the language or a limitation of the DateTime granularity or something?

This can be demonstrated using the following code:

        DateTime then = DateTime.Now;
        Thread.Sleep(1234);
        DateTime now = DateTime.Now;
        TimeSpan taken = now - then;
        string result = taken.TotalMilliseconds.ToString(CultureInfo.InvariantCulture);
        //result = "1235.1235"

As commented by CodesInChaos:

DateTime` isn't accurate to this level of precision: see C# DateTime.Now precision

However - that doesn't quite explain this behavior.