RobertMac, unless you believe ALL cattle born and raised in the USA are top quality, then it is pretty easy to see that some cattle, in each breed and age group MIGHT produce better beef by being fed some amount of grain. Further, that they might be turned into better beef in a shorter time period.
Re. the "cardboard" taste of McDonalds' burgers: it might be interesting to consider the way the meat is handled and cooked. Could the same burger meat be properly seasoned with a bit of salt and pepper, gently shaped by hand rather than stamped into a thin, dry 'puck', and grilled properly and come out tasting very different than the usual McD's burger?
If so, wouldn't that be proof that it isn't the quality of the actual meat that is the problem, but the preparation method?
Re. grass-fed versus grain-fed, I'll be quick to state that I've not eaten grassfed from very young animals fed solely on green and growing grass. I most often eat grassfed beef from cattle that are age 2 years or (most often) older. I believe that gives a different flavor, almost gamey, some say. It is also less naturally tender unless well aged. The most we are able to get it aged is 14 days. I would much prefer 21 to 28 days, but just don't have anyone in the area who will do that. What is the typical aging time of most beef promoted as grass-fed?
RobertMac, and others here who sell it, how long is your grass-fed beef aged, and what age is it when slaughtered? Is it always fed green, growing grass? What is the size of the pastures/paddocks? Is it naturally renewable native grasses on continuous sod, or is it annually planted grasses and forages? I feel all that is important, as it, along with slaughter age and other feed can indicate whether an animal has distances to walk for exercise that make muscles develop fully. Wouldn't those factors have a bearing on tenderness and flavor of the meat?
Re. why more land isn't used to grass finish cattle: weather, including high and low temperatures, but maybe more importantly, annual amount and timing of precipitation and length of growing season, profitability of alternative 'crops' and land taxes. In other words, what can one grow and make a living from, given his own expertise, knowledge, and interests, yet be a good steward of the land and wildlife?
mrj