True, those snare, kick, and tom hits were recorded in isolation, without any other drums being played. And there is not an assumption on my part. I've mixed songs using samples on top of the existing drum tracks. The drums were atrocious; it was necessary.
The main benefits of a well-recorded sample are that there is no bleed from other drums, and the ability to layer multiple samples onto the snare. For example, it's quite common to mix the recorded snare sound, plus a sample of a snare that has a good "crack", plus a sample of a snare that has good bottom end. So, three snare sounds going at the same time. This is technically sample enhancement, not sample replacement. And that's why it sounds like the Incredible Hulk is slugging the crap out of the nicest snare drum you've ever heard.
And there is another benefit: now that a significant part of, say, the snare sound, is coming from samples, then you are even more free to aggressively EQ and compress the hi-hat and/or other cymbals. Normally the bleed into the snare mic would prevent such aggressive tweaking. However, the bleed into the snare mic isn't a problem anymore, because of the samples dominating the snare sound.