In fact, the default value is 450 MiB, which is obviously not divisible by 1024, but still, I don't think Core developers would put a default value that would make RAM be used inefficiently.
In fact 450 MiB is obviously divisible by 1024.
450 MiB = 450 x 1024 KiB.
450 MiB/ 1024 = (450 x 1024) KiB/1024 = 450 KiB
Or 450 MiB/ 1024 = 450 (1024)2 Byte/1024 = 450x1024 Byte = 460800 Byte
Core developers has highlighted this in their doc saying that dbcache parameter is specified as MiB(1024) indicating that memory must be measured in binary units rather than in decimal ones.
You are right, I will change it in my OP. Because, actually, any number can be put in the dbcache option. Any number is divisible with 1024 since it's measured in MiB.