Tuning Oracle IO

I was reviewing the Oracle Tuning documentation and noticed something very confusing. In chapter 20, Tuning I/O it states:

"Separating Tables and Indexes
It is not necessary to separate a frequently used table from its index. During the course of a transaction, the index is read first, and then the table is
read. Because these I/Os occur sequentially, the table and index can be stored on the same disk without contention."

Wow. Everyone I have talked to has said separate indexes and data on different drives. Why would Oracle issues such a misleading statement in their tuning documentaion. Are they correct? Any commets?

• Allen