The way I'd think about it is "would that business put any time into a partnership with Apple/Amazon if the chance came up". I guess you could argue that any business above a certain size would consider them worth talking to for some kind of cross-promotional deal even if that doesn't make a lot of sense on the face of it - Caterpillar? Hilton? But I think small focused companies outside of Apple/Amazon's core field wouldn't want to spend time on something like that. So B2B, non-tech, smallish companies - which by their very nature I can't name a lot of, but there's a lot of them out there.
In economic theory there is no benefit to diversification (which is what a company does when it absorbs another company) unless there are organisational improvements shared between the companies. If the acquired company is truly completely unrelated there would be no benefit at all as Apple isn't able to improve the running of an unrelated company. Being bought out by Apple might be a nice outcome for any company's shareholders (as they might get a premium on the their share prices), but technically there would be no improvement to the business in terms of expected revenue.
