Wow, haven't seen that before.
Judging by how deep the crack goes I'd guess that there is a delam between within the core which led to the split occuring. Judging by the location of the crack I'd say its most likely between the edge of the wood core and the plastic sidewall. If this is the case then I'd say its a manufacturing defect or a flaw in the engineering of the ski. There are a couple of possible causes if his is the case:
One, there was a 'dry spot' between the sidewall and wood which would grow under load and lead to failure between the sidewall and wood core (which in turn lead to the crack in the base). This would be a manufacturing defect as there shouldn't be dry spots (dry spot is simply where there isn't any adhesive/glue).
Two, I'd guess the sidewalls are made from a UHMWPE (like P-Tex). UHMWPEs have low surface energies (i.e. not sticky) which makes it hard to get a good bond to the material. This is countered by choosing an adhesive designed for the sticking low surface energy plastics. If they didn't use such an adhesive then the joint would be weak and readily fail. This would be a materials selection mistake. Another way of getting around the low energy of the material is to treat it using a variety of means to increase its surface energy. If they didn't do this then it could also be considered a design flaw. If they were supposed to be treated but for whatever reason your sidewall didn't get treated or weren't treated sufficiently then it would be a manufacturing defect. Its also possible that some sort of grease/oil type substance ended up on the sidewall which would stop the the glue adhering properly (manufacturing defect).
I think you might have a legitimate case for this ski failing as a result of the manufacturing or design flaw. The only problem is this is going to be very hard to prove without the right equipment. Also I don't think that there are any manufacturing standards for skis so whether they decide to replace it or not would be based on whether they thought keeping you as a customer happy is worth more than the cost of giving you new skis.
