As others have already stated, this is correct.
From Delta's website:
We try our best to accommodate all baggage needs; however, bags that do not meet our size and weight restrictions require special handling and additional fees.
Note that you will incur separate fees for exceeding our size, weight, and quantity limitations. For example, if an extra piece of baggage exceeds the weight and size limits, it will be subject to three fees: one for the extra bag, one for exceeding the weight limit, and one for going over the size restriction. Fees are charged for each additional bag, each way.
http://www.delta.com/traveling_check...gage/index.jsp