That's incorrect. Any base system has the same property. For base 12, we would just have two extra digits, and we would be counting powers of 12 instead of powers of 10. Let's say those extra digits are X for ten and Y for 11. We would write numbers like so (starting with zero and incrementing by one): 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, X, Y, 10, 11, 12, ..., 18, 19, 1X, 1Y, 20, 21, ..., 29, 2X, 2Y, 30, ...

For example, in base 10, a number 265 means we have 10² twice and 10¹ six times and 10⁰ five times (100 + 100 + 10 + 10 + 10 + 10 + 10 + 10 + 1 + 1 + 1 + 1 + 1).

Same number in base 12 has 12² once and 12¹ ten times and 12⁰ once (144 + 12 + 12 + 12 + 12 + 12 + 12 + 12 + 12 + 12 + 12 + 1).

A "round" four-digit number in base ten is written as 1000 (written in base twelve as 6Y4). If we subtract one, we get a three-digit string of nines (highest single digit): 1000 - 1 = 999 (written in base twelve as 6Y3).

A "round" four-digit number in base twelve is written as 1000 (written in base ten as 1728). If we subtract one, we get a three-digit string of Ys (highest single digit): 1000 - 1 = YYY (written in base ten as 1727).

I hope this shows you how there's symmetry between the bases and there is nothing special about base 10 other than we're familiar with it. If we were familiar with base 12, the "round" numbers for us would be (writing in base 10 here): 12, 144, 1728, ... which we would be writing as 10, 100, 1000, ...