Array.Count() much slower than List.Count()

When using the extension method of IEnumerable<T> Count(), an array is at least two times slower than a list.

Function                      Count()
List<int>                     2,299
int[]                         6,903

From where did the difference comes?

I understand that both are calling the Count property of ICollection:

If the type of source implements ICollection, that implementation is used to obtain the count of elements. Otherwise, this method determines the count.

For the list it returns List<T>.Count, and for array, Array.Length. Moreover, Array.Length is supposed to be faster than List<T>.Count.

Benchmark:

class Program
{
    public const long Iterations = (long)1e8;

    static void Main()
    {
        var list = new List<int>(){1};
        var array = new int[1];
        array[0] = 1;

        var results = new Dictionary<string, TimeSpan>();
        results.Add("List<int>", Benchmark(list, Iterations));
        results.Add("int[]", Benchmark(array, Iterations));

        Console.WriteLine("Function".PadRight(30) + "Count()");
        foreach (var result in results)
        {
            Console.WriteLine("{0}{1}", result.Key.PadRight(30), Math.Round(result.Value.TotalSeconds, 3));
        }
        Console.ReadLine();
    }

    public static TimeSpan Benchmark(IEnumerable<int> source, long iterations)
    {
        var countWatch = new Stopwatch();
        countWatch.Start();
        for (long i = 0; i < iterations; i++) source.Count();
        countWatch.Stop();

        return countWatch.Elapsed;