Yes the hamburger is just the scraps grounded up. At the supermarket where I worked at would get in what they called course ground 10# tubes while we ground the meat we added in all of our beef trimmings. We had a 73/27 mix, a 80/20 mix (ground chuck), and a 90/10 mix (ground sirloin). The only difference was the amount of fat content. But today's supermarkets rarely grind their our meats it all comes in prepackaged. So your meat market guy is not even the meat cutter anymore. It sorta our industry where we have part changers instead true mechanics.
As for taste beef is a lot like pork different parts taste differently. Now a sirloin streak and a sirloin roast would taste very much the same due being same meat but the cooking method does affect taste as do the bones. It is like deer here I don't deer steaks but the same meat ground into burger meat is edible to me. The grinding actually affect the taste.
This like boneless pork chops and a boneless pork loin. It is the same meat. Just like country style pork ribs, pork steaks, and a Boston butt (upper front pork shoulder) is all cut from the same piece of meat. Now bone-in pork chops and the sirloin chops are from the backbone same boneless pork loin except the bones adds a different layer of taste. Here I never buy boneless pork chops, just the whole or half loin and slice it up myself this way I can control whatever thickness I want.
So if you wish to save some money you buy the roast and slice it into steaks yourself after it is near freezing temps (which stiffens the meat and make makes easier to slice).
As for hamburger you would be a lot healthier if you grind your own as you know exactly what is in it where that grounded beef from the store is just about anything including bad parts.
And you definitely don't want to know what is in your favorite hot dogs and bologna.
