Performance tuning: Rows or blocks?

In today's article from Ric Van Dyke he teaches us some of the finer points of performance tuning by making us question some "conventional wisdom" about tuning for rows.  With a great example showing two identical tables that have their data packed differently, he is able to show how the focus on row returns is not always the best idea for SQL performance tuning.  Why is this so important?  Ric gave a great talk at Hotsos this year that opened my eyes to how Oracle deals with blocks and combined with the information in this article gives me a better idea of how to measure and tune our performance!