System catalog future changes

Hello again,

Reading a previous recent post and answers called "Describe Table" got 
me thinking about a little piece of SQL I use in an application to get 
a list of all the tables for a specific namespace:

select pg_class.relname as table_name
from pg_class join pg_namespace on pg_namespace.oid = relnamespace
where pg_class.relkind = 'r' and pg_namespace.nspname = 'public'
order by pg_class.relname

I have assumed that this sort of query would be relatively "durable" - 
that future system catalog changes are unlikely to make this query stop 
working? Does anyone have any knowledge of how "fixed" the columns and 
values of this query are (i.e. are there a lot of internal and external 
dependencies that make future Pg versiosn unlikely to break the above 
code)?

Any other input on the above SQL - should I be doing this in another 
way?

Thanks for any thoughts or advice,

Steve