That was my thought when I was reading the article. On-chip SRAM on microcontrollers feels different because on general purpose CPUs the generic programming model has registers and RAM with the cache managed for us by others. On MCUs you almost always end up being aware of on-chip SRAM and off-chip SRAM or DRAM. The lines are blurry for larger MCUs but for lower end stuff like Cortex M, AVR or MSP430 it's definitely a good idea to look over instruction timing for all the different flavors of storage.