Took a taxi this afternoon in Ixtapa. Should be 70, but they all charge 80. I'm tired of arguing with them so now I just pay and don't tip. So I'm paying the same I would have tip included. So I hand him a 100p note and he hands me back a US 1 dollar bill and asks OK? I just laughed and said, yes, I can use it in April when I return. There is no change in Ixtapa! (or Zihua)

You just gave a perfect example of (a) why NOT to pay in dollars, and (b) why they price gouge foreigners. I hate to see them do that to you or anyone.

If those are the posted rates, why are taxi drivers charging more?

Besides price gouging people who don't know the rates, please see the explanation to your question in the text above the rates on the page I linked to. Don't take taxis at hotel taxi bases. Catch them on the street.

I see that there are taxi rates posted on this site from February 2023. Is there a current updated rate schedule for taxi fares?

They are the current updated rates. No rate increase has been authorized since then.