Thank you for your post, but with all due respect, me thinks you misunderstood me. I was talking about balance shafts not counter balancing a crankshaft.
Everything you said about the crank is absolutely correct, however, as I understand it, straight 4's have secondary motions (side-to-side IIRC) that create the traditional buziness/harshness that has been typically associated with 4cyl engines.
Awhile back some engineers decided that if they put a "balance shaft" in the engine that is on an eccentric it will offset/reduce these secondary motions of the traditional inline 4cyl engine. IIRC these balance shafts turned twice for each single rotation of the crankshaft.
Hope this makes sense.