The assumption is that Apple is saving money by using recycled aluminum, and is putting the savings it its pocket. Accepting the notion that using recycled aluminum reduces Apple's costs (which may or may not be true), it's just as likely that Apple is using the savings to pay for some other new feature, or to offset the increase in cost of other components. That's the way all manufacturers operate. While Apple is legendary for its higher prices, even Apple has to keep those prices within a range the public will be willing to pay.
Sure, "Apple is pocketing the savings" fits neatly into the "Evil Apple" narrative. If you want to believe the company is 100% evil and that there's evil intent in everything it does, there's not much I can say that would change your mind.
But if you're interested in another explanation...
It's likely that machining and other manufacturing costs for those 100% recycled aluminum cases far exceed the cost of the raw aluminum, so if Apple is saving any money at all, it's likely to be pennies per Mac. It's also likely that prior to "100% recycled aluminum" there was already a fairly high percentage of recycled aluminum in use. Sourcing "certified 100% recycled" aluminum may actually cost Apple a bit more than if they were willing to use aluminum with an unspecified amount of recycled content.
Regardless of the recycled content, Apple will have specified the metallurgical properties of the aluminum - a specific alloy. Yes, there are various sorts of "aircraft grade" and such - but those are not dependent upon the percentage of recycled content, but upon chemical composition and processes like heat-treating. "Aircraft aluminum" is not produced from virgin aluminum from a particular bauxite mine, it's produced by cooking up a particular soup in the smelter. If you read this page about aluminum alloys from the aluminum industry, you'll see that there's no mention at all of recycled content - alloying is dependent upon other factors:
https://www.aluminum.org/resources/industry-standards/aluminum-alloys-101
Here are some other interesting quotes from that website (emphasis added):
Secondary production (aluminum produced from recycled material) saves more than 90 percent of the energy required to produce primary aluminum. Secondary and primary aluminum are chemically indistinguishable from one another.
The metal is 100 percent recyclable without loss of the metal’s properties. Recycling is also widespread. According to a study by Delft University of Technology in 2012 in Seattle, WA, more than 90 percent of aluminum in buildings is recycled.
And finally, this:
Companies across the country are incorporating environmental and sustainability goals into their business mission statements.
Apple has pioneered the use of aluminum to create a sustainable and environmentally responsible manufacturing process. In 2007, Apple CEO
Steve Jobs released a letter recommending changes to the company’s environmental policy to achieve “a greener Apple.”
Jobs specifically encouraged the company’s adoption of aircraft-grade aluminum to improve recycling uptake. At that time, Jobs forecasted Apple would increase recycling effectiveness from 9 percent in 2006 to 28 percent in 2010. This goal was surpassed. The company achieved a 66 percent recycling rate in 2009 and has set a goal of 70 percent for 2015.
I believe what that emphasized part means is that by using higher-quality aircraft aluminum, Apple found a better market for the waste aluminum generated during manufacturing.
