why is there no TRIGGER ON SELECT ?

Other than "It's currently not available", can anyone provide a logical explanation of why triggers cannot be implemented for SELECT statements, or rules for SELECT must be DO INSTEAD SELECT?

PostgreSQL was derived from Ingres, and Ingres had a nice auditing feature that also handled SELECT.  It would be simple enough to write a RULE or TRIGGER on a SELECT to just log access, but for some unexplainable reason (at least to my knowledge) this has been greatly restricted in PostgreSQL. I am sure many DBA's and developers would greatly appreciate the addition of a TRIGGER or RULE on SELECT, and it should be simple enough to change the code, so I am curious as to why this has never been done.

Thanks in advance.

Melvin Davidson