No, exactly. I got a free battery replacement on my Macbook Pro after 3 years of having it because the battery was unusable.

After going into the Apple store, they said that the battery was a "consumable part" and therefore not covered by the warranty. However, when I asked what the part number was and how I could order a replacement myself, they said that the batteries weren't serviceable and even they had to replace the keyboard unit as that contained the battery and it was all glued together.

I pointed out that they've therefore designed this product to fail after a few years as you can't order replacement batteries as a consumer, and they agreed to replace it for free.

Yes, of course it is. Most users can’t replace tires, spark plugs, or even oil in their cars. Parts are considered consumable if they are reasonably expected to be consumed during normal operation. No court is going to hold a company liable for basic physics.