Why are skill speed & spell speed separate stats?

[Giantbane]

I think that is just bcoz the abilities are base on TP (Weapon Skill) or MP (Magic Spell).
For example when a WAR cannot use WS, he still can cast Flash.

Skill Speed reduces the GCD and Spell Speed reduces the casting time.
Flash, sword/shield oath are instant cast spells, I think Spell Speed also no effect on them.

Well, yea I get how it's working now.

I don't understand why there's not one single stat "Speed" that reduces both GCD and cast time. Every other secondary stat works on all skills, whether they're based on TP or MP.