Why are skill speed & spell speed separate stats?

[Grey_Cain]

I think you have answered the question by mentioning Flash for example.
If flash is affected by Skill Speed, then you may cast it more frequently, apparently the system was designed to restrcit you to do that. ^^

Well, no, because you can still stack Spell Speed to cast Flash more frequently; it's just harder to do because tank gear tends to come with only Skill Speed. To your previous example, instant-cast spells like Aero and Scathe still benefit from the GCD reduction, so there isn't really any difference between the two stats except one is for spells and the other is for weapon skills. BRD songs are another example where they have to separate stacking between Skill Speed and Spell Speed (if they actually wanted to) to get GCD reductions on all of their abilities.