Why Mage::getModel() is not using for resource model classes?

Question

This is a code snippet from app/code/core/Mage/Catalog/etc/config.xml.

<config>
..............
    <global>
            <models>
                <catalog>
                    <class>Mage_Catalog_Model</class>
                    <resourceModel>catalog_resource</resourceModel>
                </catalog>
                <catalog_resource>
                    <class>Mage_Catalog_Model_Resource</class>
                    <deprecatedNode>catalog_resource_eav_mysql4</deprecatedNode>
                    <entities>
                        <product>
                            <table>catalog_product_entity</table>
                        </product>
................
</config>

We can create Mage_Catalog_Model_Porduct object as

$model = Mage::getModel('catalog/product');

Same way can create the resource model object as follows.

$resourceModel = Mage::getModel('catalog_resource/product');

I know basically there's already a function as Mage::getResourceModel();. Example: Mage::getResourceModel('catalog/product');

But this way is also works fine.

Can anyone explain why not using Mage::getModel() to get the resource model object ? Any suggestions will be appreciated.

Answer 1

This is just my opinion so feel free to challange it, but I thing it's because in theory you can change the resource model class. For example I can add in my own module this:

<global>
        <models>
            <catalog>
                <resourceModel>my_resource</resourceModel>
            </catalog>
            <my_resource>
                <class>My_Module_Model_Resource</class>
....

If I were to use Mage::getModel('catalog_resource/product') I would get and instance of the original class because in the config DOM the declaration still exists.
but by calling Mage::getResourceModel('catalog/product') now I get and instance of my new class.
So I can conclude that the reason it 'extensibility'.
An other reason could be to keep a consistency.
If you call Mage::getModel($someParam) you will get the corresponding resource model by using the same parameter : $someParam.