Why are "the teens" special ?

From: elevans1
Message: 46561
Date: 2006-11-11

While using this web page:
http://ihor5.freeyellow.com/slovcipher.html
to figure out the date my great-great-great-grandmother was born
(that's her record listed as an example, the web page owner wanted to
post it as an example after I wrote to thank him for his page), well,
I became intrigued with this concept of treating at least some teen
numbers different from "the norm" in some Indo-European languages, and
I wondered if anyone could explain to me the root cause for this?

Reading his explanation for these Slavic Ciphers, his last paragraph
before the examples states that the teens need to be treated
differently from all other numbers. For example, the number twelve
needs to be written "vi" (2 + 10) instead of "iv" (10 + 2). He says
it has to do with the way the teens are SAID, "dvenadtsat", with the 2
first and the teen last. But numbers higher than the teens, for
example, the number 21, would be written "normally" (also as they are
pronounced), first with the tens' place then with the ones' place
(first "twenty" then "one").

Then I was thinking that to some extent, English is like that, not for
11 and 12, but we say thirteen with the 3 first and the teen second.
For numbers in the twenties an higher, we say the tens place first,
and the ones' place second: "twenty one". Then I remembered way, way
back, taking Spanish in junior high school. It seems to me that the
numbers 11 thru 15 are said differently, starting with the one's place
at the beginning of the word. But numbers 16 and above start with the
tens place.

The only language I have started to learn that is not Indo-European is
Hungarian. In Hungarian, there is no exception for the teens, 11 is
basically "ten and one", twelve is "ten and two", twenty one is
"twenty and one", etc. All the 2-digit numbers seem to follow the
same naming pattern, with the tens' place first and the ones' place
second. How logical!

Can anyone discuss the reversed-number names for the teens (or at
least some of the teen numbers) in Indo-European languages? Did the
teens have any special significance in the past? Or is it simply
something like more common words being the most "irregular", with
numbers that were used less often following a more regular pattern?
Did the concept of "tens' place", etc, come much LATER, after the
lower numbers had been named?

Please bear with me, this is my first post. I am not a linguist, I'm
just an average person with maybe more fascination with languages than
most people have. Still, I would be grateful if someone could reply
at a level that I might understand. I am trying not to interrupt with
stupid questions, I have tried several times to search this forum to
see if someone has already discussed this, but I haven't found anything.

Thank you for your patience,
:) Elaine