Validation Methods

The example list at the following link: Validation shows the following example of using the validate function:

validate: function (attrs) {
    for (var key in attrs) {
        var value = attrs[key];
        if (key === "title") {
                        if (value.length <= 0) {
                            return "Error: No title!";
            }
        }
    }
    if (key === "author") {
        if (value.length <= 0) {
            return "Error: No author!";
        }   
    }   
},

My question why iterate through the attrs array when you can just access the properties of attrs using dot syntax, i.e. "attrs.key". For example, I could access the properties of the passed in attrs using the following dot syntax if the "key" property was part of the passed in attrs:

validate: function (attrs) {
        if (attrs.key === "title"){
            return "Error: No title!";
        }
    },

Is there some reason I should be iterating through the array like the example in the documents show?