Steven Sinofsky responds to the fall of Blackberry on his blog:

Disruption happens when a new product comes along and changes the underlying assumptions of the incumbent, as we all know.

Incumbent products and businesses respond by often downplaying the impact of a particular feature or offering. And more often than folks might notice, disruption doesn’t happen so easily. In practice, established businesses and products can withstand a few perturbations to their offering. Products can be rearchitected. Prices can be changed. Features can be added.

What happens though when nearly every assumption is challenged? What you see is a complete redefinition of your entire company. And seeing this happen in real time is both hard to see and even harder to acknowledge. Even in the case of Blackberry there was a time window of perhaps 2 years to respond-is that really enough time to re-engineer everything about your product, company, and business?
…says the man who left Microsoft.
His post is decent, but hindsight is 20/20. It’s like an alcoholic with a revoked driver’s license telling you not to drink and drive.
Sinofsky mentions “Christensen” once, but it would have been good to mention the actual book that obviates his blog post—The Innovator’s Dilemma by Clayton Christensen.