SQL Server Table Index To big
Your problem is not the primary key.  It is a misunderstanding of what a clustered index is.  If you look at your structure you will see that the primary key is clustered.  This is the default and fairly normal but is not always the case so it pays to check.  

The clustered index is basically the table itself.  The data pages of the clustered index are the data pages of the table.  So your 450mb for the primary key is mostly the data of the table itself.  At 446264K that makes it about 1k per row which is not unreasonable depending on the amount of data in the AuthorURL and Comment columns.