That's not the importance of the case. True, Ezreal can equip Kleptomancy, but that means he's trading more burst damage potential of Electrocute from other rune paths for the sake of utility in its entirety! Skirmishers can equip Glacial Augment, but they trade the bonus sustain potential of Lethal Tempo for the sake of utility! Etc!!!!
But for healer/shielder supports who scale with AP, such as Soraka, Janna, Morgana, etc, they would love to be able to relish in utility runes with a dash of AP on the side, yeah? Well, thanks to some genius, that isn't allowed to happen. Supports will either have to give up on Summon Aery and 27 ability power, or they'll have to sacrifice Cosmic Insight and Magical Footwear, just to be allowed to use Revitalise!
Do you understand the difference with healer supports than your other examples? They have to sacrifice the utility they need for heals just so they can have a rune that assists in healing! It's counter-intuitive, and it hurts supports that don't need to build tanky to be effective.