Look at it this way...
In baseball, a perfect game is really just the best kind of no-hitter, but we still keep stats on perfect games because it is so completely rare and wonderful. If somebody pitches a perfect game, we still categorize it as a no-hitter, but it also gets its own category because it's the best kind of no-hitter. Plus, you rarely hear somebody refer to a perfect game as a 'no-hitter'....it's called a perfect game because it deserves it's own name. Technically, you can lose a no-hitter but you can never lose a perfect game. (NOTE: Technically, with the new extra inning rules in MLB, that's no longer true, but it's been true for well over 100 years.)
In poker, a royal flush is really just the best kind of straight flush, but we still keep stats on royal flushes because it is so completely rare and wonderful. If somebody gets a royal flush, we still categorize it as a straight flush, but it also gets its own category because it's the best kind of straight flush. Plus, you rarely hear somebody refer to a royal flush as a 'straight flush'....it's called a royal flush because it deserves it's own name. Technically, you can lose with a straight flush but you can never lose with a royal flush. (barring games with wild cards.)