Advanced inventory management systems use this logic. If Joe Blow in a non-competitive market pays more for their w connecting on that flight than jane smith on another routing that connects on the same flight, would you want to give them both the same inventory? Imagine the possible number of connections that may fly on that segment. The W fare is not the same in every market...each marketed city pair has it's own fare value, and the ones that are worth more get more availabilty.

Now in this case, the same markets exist, so in theory the same fare for w is on both flights...but if the other LAX-ORD is a high demand flight and "w" is not available, then it isn't available on the other "married" segment(segment that is attatched to it via your availability check. If you try to cncl 1 segment and piece your itinerary together, it will not give you a valid fare. If you wanted to "break your fare" and pay point to point for each leg, you could book each leg individualy, but you would NOT get the benefit of the LAX fare, rather you would pay the LAX-ORD fare plus the ORD-DUB fare.

This is common in so much as it happens every single time on many airlines.