The base effect of Expeditious Retreat is a movespeed bonus effect. In the case of that spell it happens to be 50%, but it could be any amount.
That would be like saying Cure Light Wounds and Cure Critical Wounds are the same because they both apply the same healing effect.
I just want people to think in terms of rudimentary effects, not spells. Think of it as imagining your own spell from scratch, not "make a song that casts fireball on every enemy."
