You will only be able to get HD resolutions on HDMI with HDCP support. Component video outputs are limited to 480p for copyrighted content because there is no copy protection.
Playing HD movies and TV shows on your Roku player
Both Netflix and Amazon Video On Demand offer high-definition (HD) content. To play HD content you must:
1. Own a Roku HD player (also known as the Netflix Player) or HD-XR player.
2. Use an HDMI or Component video cable to connect your Roku player to an HDTV.
YouÃ¢â‚¬â„¢ll know that youÃ¢â‚¬â„¢re getting HD when the Ã¢â‚¬Å“HDÃ¢â‚¬
I can confirm that I get the "HD" logo when streaming HD content from Amazon or Netflix using component.
I did switch my Roku to HDMI to see if I could see a difference.