The difference being that Microsoft supports their operating systems for up to/beyond a decade security/support-wise, for the most part...even including many of their software products.
Apple? They have no claimed policy. Historically they have supported only 2-3 of the last Operating Systems released.
Now also take into that Apple pulls support for older apps that no longer receive updates, and you actually risk losing an investment in a software ecosystem that you might depend on in as little as 3 years with OSX.
AND, Apple has no stated support guarantee. Period. So really you're at their mercy depending on how they feel in terms of an ecosystem that supports legacy environments.
But that also seems by design. There are probably people that LIKE this strategy; as it keeps their systems fresh and modern. Can't fault that philosophy.