Nope, I don't like DC's explanation. Seriously: "I mean, every seven years would be a little bad." Yes, having sex only once every seven years would be bad for most HUMANS. But Vulcanians aren't humans. I say let them be alien. Let them have a strange sexuality.
My view that Vulcanian males only have sex during their Pon Farr. They must return to a specific place on the planet Vulcan to complete this ritual. I think we tend to focus only on the seven years cycle and completely forget that the place is just as important as the time. The entire premise of Amok Time is based on this.
The only thing known to disrupt that seven year cycle is stated in "The Cloud Minders" which is "extreme feminine beauty". So there may be rare occasions when the seven year cycle is disrupted, but for the most part it's the rule.
I've always liked the concept that Vulcans only mate once in a seven year cycle! They are aliens and have a much longer life span than humans! Plus I've read the theory earlier on that maybe they become fertile in that seven year cycle which I think was very clever too!
DC Fontana wrote Amok Time she set up the fictional culture so I'll take the creators word for it.
That's funny, I thought it was Theodore Sturgeon who wrote Amok Time! I'm sure it's got his name on it!
JB