Apple does use an extra microcontroller or small processor in MacBooks and other machines that controls fans and probably a large number of other power related things. They call it the SMC:
Everybody does that. This has not much to do with ACPI. ACPI is mainly a software thing (yes, you have some dedicated register support in some chips, but the baseline of those that are absolutely necessary is quite small and well supported by chip vendors)
ACPI has also proven to be an idea with a very bad execution: much of the tables are filled with bugs, and the spec has been written by complete psychopaths. IIRC sometimes it is better to skip entire sections and to use a custom written driver for each OS (like Intel did for some processors or chipsets for Linux I think)
Remember that ACPI has been created in part by MS, and that Bill himself wanted a conception that was easy for windows and hard for the other. I'm not sure this has been executed for the conception (even though the result is a mess), but MS absolutely managed to create an ecosystem where board vendors test only on Windows and ship if this kind of work, regardless of the amount of obvious bug present in their ACPI code.
http://en.wikipedia.org/wiki/System_Management_Controller
So maybe not ACPI, but homebrew.