Why is a digitizer the 'proper' way to do it? Because the marketing people say so?
Because resistive UIs suck at responsiveness. Anyone who used a resistive and a capacitive screens knows that. It's precisely why e.g. Windows Mobile was so stylus-centric - because with resistive screens, you pretty much had to use a stylus. Or at least something sharp, like your nails. Or cuss every time you try to press a touch button and it wouldn't register.
Why should I have to carry around some expensive second piece of hardware when my finger does the trick just fine with a resistive touch screen?
Usually, if a device has a digitizer, it has a stylus in the box (so you don't pay extra for it), and it also has some place to stow it away.
Why should I be locked into Samsung? I just had a Samsung phone. It sucked bad, it locked up or slowed down almost constantly.
Who says anything about being locked into Samsung? There are plenty of manufacturers who do digitizer-enabled phones and tablets these days, on various OSes.
Anyway, digitizer is certainly the most popular way to achieve this, but it's not the only way. The other option is to actually make capacitive screens that let you use pencils and ball pens (or something similarly sharp and conductive) on them without damaging the screen. An example of that approach is Sony Xperia Z Ultra, but I suspect we'll see more of it, now that the coating they use is on the market.