This is where I disagree. The differences between a CB/OB and CB/rail collision are significant enough that they do warrant separate terminology.
From a physics perspective, they are about as different as two collisions involving a smooth, rigid sphere on a level playing surface can be: ball to ball collisions approximate elastic collisions between objects of equal mass, conserving kinetic energy and momentum, whereas ball to rail collisions are obviously inelastic due to the rail compression and between objects of (very) unequal masses. Sure, there are still minor effects due to friction and compression between balls, but not of anywhere near the magnitude of those effects off a rail.
More importantly, the application of these collisions to the game of pool are very different, even if you just limit the discussion to the use of spin. I think we can agree that the primary use of CB spin in pool is for playing position off the rails. For that interaction, it makes sense to use terminology that focuses on the effect on the CB: running and reverse/check do exactly that. For CB/OB collisions, the effects of using english aren't really specific to one aspect of the shot; it affects the initial path of the CB, it causes swerve on the CB, it causes/cancels throw/spin on the OB, it may eventually affect the path of the CB off of a rail, etc. Instead of trying to sum this all up in the terminology, we simply describe the spin in terms of the angle between the CB and intended OB directions using the terms inside and outside.
I concede that it would be possible to establish an inside/outside convention to describe the spin relative to contact with a rail, but the reference angle isn't as obvious in that case as it is between two balls. Am I referring to the inside or outside of the angle between the rail and the incoming ball, the angle between the incoming and outgoing ball, or the angle between the outgoing ball and the rail? With running and reverse/check, there is no ambiguity.
Using running/reverse/check to describe the spin of one ball relative to another is actually more precise, but is based around an effect that doesn't really factor into the shot selection. How often are you playing a shot with english for the sole purpose of increasing or decreasing the speed and angle of the CB off of the OB? If at all, I'm sure it's far less often than you are using english to throw the object ball, which, in turn, I'm sure is far less often than you are using english to control the cue ball path off of a rail after OB contact.
