Danger exists in more places than just in front of you. A proper driving education taught me to scan my whole surroundings while driving... not lock eyes with the road in front and never blink. I am not looking directly in front of me 100% of the time. I am looking front, left, right, behind, at instruments... and repeat (not exactly with any particular cadence). My eyes are always moving. Glancing at the speedo is such a minor part of it. Even with a full-on HUD, I'd still be looking left, right and behind.
EDIT: when I say "looking behind" I mean the rear view mirror. I don't physically turn my head around to look behind me. That would not be comfortable.
But even having to look down at your speedometer or odometer can be a problem at speed, considering how much distance you cover in half a second.