Space is cheap now tho. Better to duplicate some data and avoid a bunch of joins than to worry about saving a few gb of space.

It’s not that easy: you need to consider the total size and cardinality of the fields potentially being denormalized, too. If, say, the JOINed values fit in memory and, especially, if the raw value is much larger than the key it might be the case that you’re incurring a table scan to avoid something which stays in memory or allows the query to be satisfied from a modest sized index. I/O isn’t as cheap if you’re using a SAN or if you have many concurrent queries.

This system was written in 2002.

Using space to avoid joins will not necessarily improve performance in an RDBMS -- it might even make it worse.

The inverse of your statement is also true. Denormalizing the database to avoid duplicating data will not necessarily improve performance in an RDBMS - it might even make it worse.