right on.. i grew up in Argentina. and yes there's a rivalry, predominantly friendly, among things like asado, futbol, mate, etc. :) and yes, between arg/uru/bra people are very friendly with each other as long as it doesn't involve futbol ;-)

It's so friendly that Uruguayans and Argentines don't identify the other as foreign. Uruguayans didn't want to be their own country when their started their independence war, it was an attempt to not be part of Spain or Brazil and to be joined with what would become Argentina. It was the British who decided Uruguay would be an independent country. Since then in the last 200 years, they've developed somewhat distinct institutions and cultures. It's similar to the relationship between the US and Canada.