I think .us is an isolated case - the .com is still so strong there that it's been hard for the country code to break in. Much different than Canada and European countries where the country codes are at least equal in use to .com, or in the ballpark.
.mx has some things going for it, Mexico has a population over 100 million, right next to the US and it's a popular tourist destination. The extension just became available in the last year, so there is still kind of a landrush mentality about it. Bido has had a lot of .mx on auction lately so that is why the sales are being talked up. English words always seem to sell in other languages cctld's, so nothing new there. I think .mx will have a good future, I own a few myself too.