Unfortunately I have to answer with a big yes to your question about our bars being tied to major companies like AB-Inbev, owner of the Brahma Chopp you've tasted. Not only the bars but I can say for sure that mostly restaurants are tied too. The big companies here have a huge power on all instances, including political. Just to give an idea of that political power, we have very strict laws here in Brazil that ties the microbreweries hands. For example, to have a new beer on the market, the brewery have to get a licence for that beer with our Department of Agriculture (equivalent to your USDA). The fact is that this licence can take, believe me, YEARS to happens. Until there, you just cannot sell your new beer.
Besides that, the ammount of money the large companies pays the bars, restaurants and supermarkets are considerable and, nowadays, is already part of their budget.
It's a very bad scenario but that's our reality, that's why the craft beers are so underground here. Sad but true!
We (the beer enthusiasts) are trying to make our part, by supporting the local breweries and sharing as much information as we can, on blogs, social networks and with our macro-beers drinker friends. I hope someday we can have craft beers all over the place here.
Jeff at Beervana knows more about the history of big beer in the US, but this makes me think of how fortunate US beer makers are to have a relatively open system generally free of corruption. Yes, I know that the distributor and retailer relationships can be cozy, but this gives a lot of perspective, doesn't it?