I probably sound like a food snob, but when I'm thinking of beef that tastes like cardboard, I'm thinking of a Big Mac, for example. If you take all the condiments and just eat the beef only, it's pretty tasteless, IMO.
A lot of people say there is a taste difference, not just me. It's subtle though, your ordinary person may not notice or care. But I'm passionate about it because I'm big into food and I think the taste of grass fed is much better.