The opponents in question are supposed to give (the enemy) spell resistance (+7, if memory serves) against spells with speed 7 or higher. However, this requirement ignores any speed modifiers that apply to an ability: for instance, a Boggy Blast sped up by Cenarion Surge will still be resisted, while a Lighting Bolt slowed down by enemies will do full damage, i.e. only the base speed is taken into account.
This also has implications for the Heroic Sayge fight, since he has two Fortune Tellers as ‘adds’ (is that the term?) and a mechanic involving speed manipulation.