However I would still strongly contest the analogy even if the database did fit in memory (the author may be off by magnitudes themselves, as in 1997 a 2GB database was a pretty substantial, unweidly thing for most people) -- doing the simple steps of putting your data in a database instantly enables enormous flexibility in the use of that data at very little cost or overhead, with better to enormously better performance than the average person is going to yield with a flat file.

This situation (Hadoop for big data), in contrast, is about throwing away a lot of flexibility, and paying a large performance price, to add big-data scale out flexibility. It is, in many ways, the opposite situation.

A lot of people use databases to implement persistent user state on top of stateless HTTP, even if the data itself is small enough to fit into memory.

This latter use was known even in 1997. For example, the book "Database Backed Web Sites: The Thinking Person's Guide to Web Publishing" was published on Jan. 1 of that year.

So even when that advice was offered, it was wrong.