Interestingly, as explained here, straights are still up for debate. The earliest versions of poker (including the 20-card variety) didn’t count straights or flushes, and the 1864 Hoyle explains how it remained the case that “straights are not considered in the game, although they are played in some localities.” Flushes weren’t part of the earliest variants of poker, either, but here are part of the line-up of possible hands.
Since straights aren’t universally accepted, neither are straight flushes, although a footnote to the hand rankings does explain that when they are counted they should be considered as ranking higher than four of a kind. “It is strongly urged by some experts that the strongest hand at Draw Poker should be a Straight Flush, for the reason that it is more difficult to get than four of a kind.”
The “experts” are right. A 52-card deck produces 2,598,960 possible five-card combinations, with only 40 of them being straight flushes (1 in 64,974) as opposed to 624 being quads (1 in 4,165).
There’s one other point made in the footnote in favor of counting straight flushes I find kind of intriguing, namely, that doing so “removes from the game the objectionable feature of a known invincible hand.”
Without straight flushes, any hand containing four aces would be known to be unbeatable, as would a hand containing four kings with an ace. With straight flushes there still exists, of course, the “invincible” hand of an ace-high straight flush (or royal flush), which could theoretically be equaled. (This possibility is explained in the footnote.) But there’s only four of those (1 in 640,974), making it exceedingly unlikely for the invincible-hand situation to arise.
Setting aside this quibbling, though, it’s kind of curious to think of “a known invincible hand” being an “objectionable” feature in poker. The variants popular today obviously include this possibility, and in fact it is hard to imagine poker otherwise. Players know fairly frequently in hold’em, for instance, whether or not they hold the “nuts” or an unbeatable hand.
Still wondering why this feature of the game might be considered “objectionable,” I continued on to read the last sentence of the footnote, which does provide an explanation of sorts.
“No gentleman would care to bet on a ‘sure thing,’” it is explained, “and we therefore think the Straight Flush should be adopted when gentlemen play at this game.”
Ah, right. This is a “gentleman’s hand-book of games,” imparting rules both for the games and for what it means to be a gentleman.
Now, of course, one can earn a penalty for not betting the nuts when last to act. And claiming you were just being a gentleman is no excuse!