Not always the case - my 2014 MBP Retina has an i7-4870HQ CPU. According to Intel's ARK, the CPU supports 32GB RAM. However, the maximum you could spec until th

Not always the case - my 2014 MBP Retina has an i7-4870HQ CPU. According to Intel's ARK, the CPU supports 32GB RAM. However, the maximum you could spec until this year was 16GB on any model. Even worse, I got my hands on a 2012 MacBook Air with an i7-3667U CPU. The maximum those models ever went to was 8GB. This i7 also supports 32GB. Finally, the latest range-topper 15" MBP has an i9-8950HK chip that supports 64GB, double the amount Apple will solder permanently to the board for you. Part of this is due to increasing DRAM densities, and used to be a good thing with Macs - frequently the device's practical maximum RAM would be twice what Apple listed as possible, since the DRAM density doubles between the time the machine is released and you actually need to upgrade the machine. However, with the RAM now soldered, we can't benefit from the increasing densities right as we start needing more RAM. When I upgraded, I bought a Skylake laptop with 16GB of socketed RAM and the option with the CPU to increase that to 64GB down the line. 32GB SO-DIMMs only became possible this year. I've read that Apple's limits of 16GB were usually down to power draw, that adding more RAM would require more power, thus bigger batteries to keep up the marketing battery life, and it was easier to just limit the RAM to '16GB is enough'. That all said, I cannot deny that modern applications are RAM guzzlers and developers seem to revel in the glut of available memory. Still, there are situations where you need all that RAM (e.g. multi-k video production... perhaps that's where the 'Pro' in MacBook Pro came from?!), and you just can't get around that requirement.