When your market share in the consumer market is approximately 0% "saving" is not good, what you need to do is grow market share. So the question is whether an appstore which is as good as your competitors will grow market share for blackberry in the consumer market. And I think the answer it takes more than just being as good as your competitors in one area to gain market share. Perhaps if they just put out some decent android phones that had the old (patented) blackberry keyboard then they could regain some market share from the texters that hate on screen keyboards. That is the one feature they can offer consumers that will be better than the competition. "Saving" market share only applies to the corporate and government markets where they still have market share to lose.
I'm not sure how much an app store "saves" market share in government, but I do know cost is a factor. I am in government and just received a Z10 after having a 9900 for a few years. Our agency was looking to go iPhone, but AT&T literally gave us the devices FOR FREE and then a credit of about $32 per old device for recycling, so the net cost of going iPhone would have been $40,000 (400 devices at about $100 per) and the net cost of Blackberry was -$12,800 (technically -$52,800 if you count the "saved" $100 per device). IT described it to me as "status quo with better hardware, and we can kick the can of moving platforms down the line or until BB goes out of business."