Why are data files stored in /var/lib

Hello

I use version 9.5 on Linux Mint 17.3.

I had a discussion yesterday with some friends, who are sysadmins about the location of database files. In a default
installation
from a distribution (apt-get install) PostgreSQL creates a cluster unter /var/lib/. According to my colleagues /var/lib
shouldnot 
contain data that is supposed to last over time. I am aware that the location can be modified to suit the needs of
sysadminsas 
described under these links.

http://www.postgresql.org/docs/current/static/storage-file-layout.html
http://www.postgresql.org/docs/current/static/runtime-config-file-locations.html

In the first link there is a line stating that "A common location for PGDATA is /var/lib/pgsql/data". My question is if
thereis a 
specific reason for choosing /var/lib as the default for database file locations, some kind of best practices or alike.
Iassume 
that there have been discussions on the topic?

Thank you and enjoy the weekend.
Charles