It's a funny old world when being the biggest buying rather than the biggest seller gets you called a "monopoly".
The difference between Apple and the rest is that they're willing to go to suppliers and say "we'll take umpty-million of your product next year and, oh, if you don't have the factory capacity for that then here's some cash now to build the factory with".
It's not only the cash that's the difference, it's also the willingness to commit to buying a huge quantity. For most companies that'd be asking to be left with warehouses of unsold product.
And even then, there are usually shortages of new Apple kit.
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