Reinheitsgebot is one of the first and oldest consumer protection laws ever passed. It is usually referred to as the German beer purity law and was first proposed in 1487 (no typo!) and passed into law in the year of our Lord 1516. It simply stated that it was illegal to put anything except water, barley, and hops into beer. It was updated and amended into the Provisional German Beer Law which allowed the additions of yeast, wheat malt, and sugar cane (but banned unmalted barley).
In America; where bigger, faster, and cheaper are king - the use of adjuncts is the norm.
Large brewers use large amounts of corn and rice (among lots of other things like artificial flavoring, corn syrup, colors ,dyes, juices, extracts, etc.) in an effort to produce the most beer for the lowest cost. They use just enough of the Reinheitsgebot ingredients to flavor their brews without having to re-label it a malt liquor. ( Malt liquors are completely based on the fermentation of corn and rice.)
So, the next time you tip a Bud or a Coors against an imported German Pilsner, realize you are actually comparing a near malt liquor (flavored to taste like beer) to the real thing. Kinda like comparing a can of Spaghettios to real Italian spaghetti . . . Which leads to twisted thinking like- If you were born and raised only on spaghettios; are they now better than the "real" thing? (Ponder that over a pitcher, or two.) But you do have to respect the big brewers for being able to pull off a brew that is almost entirely water and still have a 3.5 to 5.5 % alcohol content. Amazing!
Thank goodness that the craft brewers have re-discovered Reinheitsgebot and its brewing principals. Brew on!