For example, IBM saw Microsoft take over the more profitable software space that sits on top of its PCs. Oracle likes to think of Salesforce as an app that just sits on top of its database, but hasn't been able to overtake the cloud-software space they compete in. Google, despite all the search data it owns, hasn't been successful in the social-network space, failing to move up the stack in the consumer-web world.
Ironically, the opposite is true when you move down the stack. Google has built a solid cloud-computing business, which is a stack below its search technology, and Apple's now building its own iPhone chips, one of the many lower stacks below its smartphone device.