why does my portrait style slide presentation
From your post, I am unable to determine if you have set up Keynote as a custom slide size in vertical format, or whether you have placed vertical objects on a horizontal slide.
If you have a slide that is horizontal, and you print vertical, the slide won't print whole page.
To print a horizontal slide, full page, select page attributes from the drop down option menu and select horizontal.
To print a vertical format slide, full page, select vertical in the page attributes.
Each print driver will look different, this is an HP printer in Mavericks: