Default model binder does not bind my model class

Question

I am trying to make a post that should use the Default Model Binder functionality in ASP.NET MVC 2 but unfortunately I can't get through....

When I click on the checkout button I populate a form dinamically using jQuery code and then submit this form to the server. This is the form that get submitted

<form action="/x/Order/Checkout" id="cartForm" method="post">
    <input name="__RequestVerificationToken" type="hidden" value="UDjN9RdWheKyWK5Q71MvXAbbDNel6buJd5Pamp/jx39InuyYIQVptcEubIA2W8DMUzWwnZjSGkLspkmDPbsIxy8EVuLvfCSZJJnl/NrooreouptwM/PaBEz2v6ZjO3I26IKRGZPqLxGGfITYqlf8Ow==">
    <input id="CustomerID" name="CustomerID" type="hidden" value="1">
    <input id="FirmID" name="FirmID" type="hidden" value="2">
    <input type="hidden" name="CartItems[0].ServiceTypeID" value="1">
    <input type="hidden" name="CartItems[0].Quantity" value="1">
    <input type="hidden" name="CartItems[1].ServiceTypeID" value="2">
    <input type="hidden" name="CartItems[1].Quantity" value="1">
</form>

This is the jQuery code that handle the submit event for the form

$("#cartForm").submit(function (event) {
    event.preventDefault();
    var form = $("#cartForm");
    var panel = form.parent();
    panel.parent().block();
    $.ajax({
        type: "post",
        dataType: "html",
        url: '<%: Url.Content("~/Order/Checkout") %>',
        async: false,
        data: form.serialize(),
        success: function (response, status, xml) {
            panel.parent().unblock();
        },
        error: function (response) {
            panel.parent().unblock();
        }
    });
});

This is the controller action that should be get called

[HttpPost]
[ValidateAntiForgeryToken]
public virtual ActionResult Checkout( CartModel cart ) {
}

And finally this is the CartModel class involved

public class CartModel : BaseModel
{
    public int CustomerID { get; set; }
    public int FirmID { get; set; }

    public List<CartItemModel> CartItems { get; set; }

    public CartModel() {
        CartItems = new List<CartItemModel>();
    }
}

public class CartItemModel : BaseModel
{
    public int ServiceTypeID { get; set; }
    public int Quantity { get; set; }
}

But the default Model Binder does not bind the web form data to a CartModel class. Using Fiddler I have been able to see that the data sent to the server is correct as you can see from the following snapshot

Any suggestion?