So you pretty much have to jump. Which is likely anyways since if you were being paid less than half than everyone else around you and doing the same or better work, you'd probably be more than a little annoyed.
Since they exist at almost every company, I think it seems probable that it's rational. Here's a simple possible argument for their rationality:
Creating big barriers to large raises/bonuses discourages employees from sharing salary info, since there's little they can do about it. Furthermore, the more your employees are worrying about their salary, the less they're working.
It's an example of bounded rationality: http://en.wikipedia.org/wiki/Bounded_rationality
The decisions seem rational given the perspective and limitations of the decision-makers.
Sure, you can talk to HR and your manager and perhaps see some form of bump in salary, but if you're significantly underpaid then a) it's likely other people are too and they won't want to rock the boat, b) there's a decent chance you wouldn't leave anyway, and c) even if you do chances are they can fill your position for what they're paying you now.