First thanks for comenting :)
Actually I said "If he takes Pyroblast expect to be the target of this ability...".
Also your assessment is not true:
http://www.hotslogs.com/Sitewide/HeroDetails?Hero=Kael%27thas
Check the statistics for talent popularity. Pyroblast is truly the less popular choice, but is still picked a little over 20% in gold league and above including masters (Stats for last 6 weeks at the moment). That is 1 of every 5 games. In my personal experience, at higher ranks 1 of every 3 games against Tracer. That is exactly due to the fact, that people pick Pyroblast to counter Tracer, since she can't escape it after Recall is forced, most players just cant time their Blink correctly to avoid it. It takes precision in parts of a second!