linked tables Access <---> PG 7.4.1

Hi,
I fear this might be off-topic but I'm sure I'd be hit, too, if I asked
something concerning the interaction with PostgreSQL on  the dark side.   ;)

Client:   MS-Access 2000
Server:  PG 7.4.1

I ODBC-link some tables and all is fine.
Then I manually link a PostgreSQL-view and Access asks which of the
fields will be the primary key of this "table".

Then again, if I link the view with VBA's DAO command
CurrentDB.CreateTableDef( [...] ) no question appears and the view gets
created as a table-object.
If I inspect it's design, there is no field marked as primary key.

Is the PK really obsolete or does it have implications in the
performance of Access or PG ?


Thanks
Andreas