var $buttons = $('.sort'), $tab = $("#tableUpdateProducts");
$buttons.click(function(e) {
    var self = this,
        $rows = $tab.find("tbody > tr"),
        idx = $buttons.index(this);
    $rows.sort(function(a, b) {
        var $obj1 = $(a).find('td').eq(idx),
            $obj2 = $(b).find('td').eq(idx),
            value1, value2;
            value1 = $obj1.find("input")[0].checked;
            value2 = $obj2.find("input")[0].checked
        return (value1 < value2);
    });
    $.each($rows, function(index, row) {
        $tab.append(row);
    });
});

[html run]
... минимальный код страницы с вашей проблемой
[/html]

return (+value1 -  +value2);

return (+value2 - +value1);

return (+value1 -  +value2);

return value1 -  value2;