Using a link to the standard login pages provides much more than just the ability to log in:

The "I forgot my password" link that allows them to reset their password online
They have to set up the Security Questions anyway; why not give them a place to use them to help themselves if they forget their password?

The "Apply for Membership" link to capture membership applications and work them right from CU*BASE (no rekeying!) 
Why would you not allow every possible opportunity for someone to say they are interested in becoming a member?

Service Alerts and announcements about upcoming changes to online banking tools
Why not let us take care of notifying your members about changes they will see once they log in?

Up-to-date education about security and what's hot
Even if you have education on your website too, why not reinforce that education in places where they are sure to see it?

Helpful tips about using online banking and related tools such as PIB
Links that answer the questions that members have on their mind