Most modern firearms, especially those of known good quality, are relatively accurate, mechanically, although some are not.
"Mechanically accurate" meaning that the firearm itself, in a machine rest, for example, will produce a tight group, and produce that group at a point of aim where the sights are aligned with the target.
However, some designs are inherently more accurate, as are some combinations of designs, while some designs, or combinations of designs, are not.
Also, the ergonomics of many designs often force adjustments which make accurate shooting more difficult. Some trigger designs just don't work well for many people, not every bore axis is conducive to repeatable accuracy, and some grip angles are simply not correct.
When you see a relatively new or different design package, (package meaning grip angle, trigger design, bore axis height, combined with the expected modern mechanical accuracy) which a considerably larger percentage of decent shooters find to be very easy to shoot with measurably better than average accuracy, you've come upon an exceptional design. It does not happen often.
It will be interesting to see where the P320 falls over time. Currently, it seems to be doing extremely well. It is however relatively new, and the recent selection as the new U.S. military side arm, as well as selection by a number of agencies local, state, and federal agencies has added to that momentum.