Place-value notation means you use a base set of symbols, and then the position when using multiple digits is a multiplier. Compared to say Roman numerals this have the advantage that you can write arbitrarily large numbers. (The Romans didn't have a symbol for numbers larger than 1000, hence larger numbers became cumbersome to write.) More important though, arithmetic is much simpler using a place-value notion, because you can place numbers vertically and then perform the operation on one row at a time.
Place-value notation requires a symbol for "nothing at this place", the "0". The post is about the oldest known use of "0" in a place-value system. (Which probably means the oldest use of a place-value system per se, since you cannot have a place-value system without "0".)
However, using a place-value notation like decimal notation does not mean that you have to accept zero as a natural number. That is a separate issue.
(It probably helped that with a base-60 system, one was six times less likely to have a zero.)
1) Dealing with '0' as an ordinary number.
2) Using a positional number system, which requires a symbol or context for telling '1230' from '1023' and '1203', etc.
One tends to think that solving the first issue leads to the second. Solving the second implies in some way having already solved the first, due to the nature of positional systems.
Untrue. (Edit: actually true). It works perfectly well to have a decimal number system using digits 1-10 instead of 0-9. For sake of notation, let's say A is the digit representing 10.
"A" = 10, "11" = 11, "19" = 19, "1A" = 20, "21" = 21, etc.
Edit: actually, I misread your argument. What you argued is definitionally true.
1. using "0" as a digit
2. using "0" as a number
I'm not sure I understand. I thought the significance of 0 was the recognition of an absence of existence. Just because numbers use 0 (270, 50, 20, etc.) wouldn't seem to indicate that it was understood at that significance...