"Most common" (i.e. statistical mode) is often such a misleading thing to pay attention to because it's so sensitive to how the person doing the study chooses to group things. For example, also on the Steam Hardware Survey, it looks like Arch is more popular than Ubuntu, but that's because Arch (being a rolling release) is only one entry, while Ubuntu is separated out into versions.

Similarly, "16GB is most common" is easily confused with "most people have 16GB," which is very much not true. It's just that the majority, which is less than 16GB, is divided between people with 4, 8, 12, etc.