Some older devices used hacks to get past the bootloader lock (e.g. my original HTC Desire: HTC did launch an official bootloader unlock, but only after the phone had been out for a year). But bootloader unlocking provided a cleaner way of doing things and solved the problem of hacks ceasing to work after software updates, so was a better solution wherever it was available.
If you have a recent Samsung then in most of the world you can unlock the bootloader, which means no need to rely on hackery. The problem is that North American models not only don't have unlockable bootloaders (probably at the behest of control freak carriers) but that Samsung have gone to great lengths to make it near impossible to do any other way. So for most models the sort of exploit that would have worked previously is no longer available.
I'm afraid the if you are in the States and interested in rooting the best advice I can give is to buy a different brand (and check first, especially if you are thinking of buying through a carrier).