Magento Group Price, Trier Price, Catalog Price and Sales Rules are different things.
Group Price, Trier Price, Catalog Price rules can be used to selectively put products on sale under certain conditions. Catalog price rules does not use coupon codes, because they are triggered before a product is placed into the shopping cart.
Catalog Price Rule -
is defining a unit price of a product and affect product view/listing pages, it works the same way as special price functionality, but on a group of products. This functionality is taken to find a final price, that is calculated on as minimal value from such options: product price, special price, tier price, group price, catalog rule price.
Shopping Cart Price Rule
is affecting a final price that you have already in a shopping card, there is no relation, if it is a rule or a tier or a group product price.
Whenever a product cart then a item in cart called as
Quote item(Mage_Sales_Model_Quote_Item) not as
product item (Mage_Catalog_Model_Product).
As per magento system coupon rules is depends on
Quote item(Mage_Sales_Model_Quote_Item) not product item Price.
Here a question it describe properly.
How to Ignore Catalog Pricing Rule when applying Shopping Cart Price Rule?