The biggest issue with the presentation of numbers like these, assuming numerical accuracy, is equating an Apple PC with a Dell PC. Not only are they apples and oranges (pun intended), it also puts a zero-sum total into the conversation. If anything, the specific quarter numbers aren't nearly as important as the trailing 8-12-16-however-far quarters to consider the trend of where things are headed.

Because Apple devices have a premium price point against those from HP and Dell, there's a natural market effect where the ceiling of Apple customers exists that doesn't apply to HP and Dell. What we don't know is where that ceiling exists, since Apple continues a near-linear trajectory growth line.

Additionally, I'm not sure that growth is a negative to HP and Dell, i.e. a customer chooses Apple OR HP/Dell, in a one-or-the-other scenario. Simply showing Apple growing it's market share here doesn't necessarily mean HP or Dell shipped fewer units.

Nonetheless, Apple is the only one on the list making material gains with its products, not anyone else.