only SELECT statements are run by Perl/DBI and that any sort of UPDATE or DELETE is run via stored procedures only.

Why might a company do this? Well, I can think of a few reasons:

Because they want the code modifying the database IN the database. Using that approach, they can build an interface that is pretty much SQL-flavour agnostic when it comes to capabilities (e.g. triggers).

It's about architechture, not about 1) performance and 2) ease of development.

/J