I intern'd at Apple and I would say that Apple's engineering talent is a level below Microsoft and Google. Apple combines good (but not incredible) engineering with the best product management (manager maybe...) on the planet. Microsoft and Google have much strong engineering teams but their much weaker on the PM side.
Then take into account all the people who do QA, all the management, marketing, business, finance, and other teams.
And you're actually left with a pretty lean engineering force. Apple engineers more stuff in house than a typical company like Dell, so that plays into the head count as well