Here is the advantage of a major over a minor at its most naked, one might say:

	A K Q 8 7 5 4
	K 9
	K 8
	8 6
9		J 10 3
J 8 6 5 2		Q 10 4 3
J 9 7 6 3		A Q 10 4 2
A 5		2
	6 2
	A 7
	5
	K Q J 10 9 7 4 3

A self-supporting 7-carder vs. a self-supporting 8-carder that just might be worthless in a spade contract. You're always going to lose a trick to the ace of clubs and a trick to the ace of diamonds. And, as it happens, whatever suit you pick, there's a singleton in a side suit that can lead to a ruff. In a spade contract, the ruffing potential is too obvious to miss. In a club, West leads his singleton, and on getting in with the ace, has to hit his partner with a diamond to get his ruff.

The moral is fairly obvious. If you're only going to make ten tricks, I guess you'd better do it in spades. Furthermore, even those declarers who are allowed a club game won't do as well as their counterparts in 4 spades.

The goat here has to be South. A rebid of two spades here tends to signal a 6-card suit, allowing an 8-card fit. Couldn't North have 5-3-3-2, the doubleton being in clubs? And no stopper in diamonds? Well, by golly, he could at that, couldn't he? But you can't spend your time figuring a worst-case scenario. What about the above suggestion that the club suit might not be runnable in a spade contract? Ditto. It might happen, but you can't spend your days foreseeing unlucky conditions.

Incidentally, I want to emphasize what I've said elsewhere that an 8-card fit is a modest fit and cannot make up for any great shortfall in hcp's. It is when you've got a clear preponderance of the hcp's that an 8-card fit is by and large sufficient to control the hand and develop all the side-suit winners you've got coming. Here, of course, it's a nine-card fit that N-S have in their major.