I have wondered about that as well. Especially about two years ago when Reactor first came on the scene, the only current balls that didn't use it were the Vertigo and Trifecta. Tropicals, Hot Rods, Banshees, Agents, Fires,... Seemed like you'd run the risk of being really screwed if you didn't like Reactor. Seemed a mighty strong cover to use on an entry-level ball, too, considering that Grooves were using PK17.
I thought the fact that you had your choice of core was neat and unique. Definitely something you didn't get with other manufacturers. Activator? Only on an Inferno or Zone. PK18? No asymmetrics for you.
SH