You cannot categorically say that HDMI has better video quality than component. Those who insist on this either a) have equipment and tested this such it makes the statement true for them or b) just assume digital > analog.
Why can't you? Assuming the digital version is offering the same or better resolution, digital is always going to be better than analog due to the lack of signal degradation. This is the case between HDMI and component. And I definitely like to see a test claiming otherwise. You can find a test claiming they are the same, but I doubt you'll ever find a serious test claiming a superior component.
And there a future considerations to worry about, namely the ICT flag, HDMI 1.3, and potential for future higher resolutions.