Why is it hard to see the value in making a product that competes in an existing profitable and developed market space, but does so better/cheaper/more conveniently? Isn't that a significant portion of the startups in YC? E.G. Hipmunk - simply a more user friendly flight search and hotel booking? Mariusz shouldn't have to spell it out for YC in this case.
If the issue is as Mariusz describes, he shouldn't be blaming himself, but rather YC instead for not seeing the obvious market potential in fairer pricing. Either YC missed something obvious or the reason YC turned Mariusz down was for a different reason than stated.
If the problem you are trying to solve is inaccessibility due to prohibitive cost, you'd have to at least show that there is market at that lower price point.
With regards to matlab, I don't believe the cost to be prohibitive. In most situations where you'd even require what matlab provides, $2k is not that much money. There is also already a very good product that competes with matlab on price - Octave, and its free.
Creating value isn't as simple as just making something cheaper.
Or it could be that YC knows Mathematica and/or matlab are thinking about launching a cloud computing service. Mathematica definitely is and it will most likely ROFLstomp whatever these guys and other competitors are coming up with. Computer algebra systems and numerical analysis aren't just topics you can sprinkle with "Cloud" dust and have it come out right. Unless these guys have years of experience, YC probably made a prudent decision.
There's obvious market potential in building a nationwide chain of stores and outpricing Costco by 1%, but an angel investor isn't going to be interested in giving you a billion dollars to make it happen. You have to have some "hook" that makes them believe you'll be able to rapidly achieve profitability and be SO much better than the competition that you have an unusually high chance of success.
If the issue is as Mariusz describes, he shouldn't be blaming himself, but rather YC instead for not seeing the obvious market potential in fairer pricing. Either YC missed something obvious or the reason YC turned Mariusz down was for a different reason than stated.