I guess I'm having difficulty understanding how the act of sex with the express desire not to conceive, employing a method to achieve that end, is "procreative"...."
In this context, "procreative sex" means sex that is the way people normally procreate. You use your sex organ too put semen in your wife's genital tract. If you're infertile for reasons beyond your control (even if you have no viable sperm in your seminal fluid, or she has no uterus, or is post-menopausal) the form of the intercourse is still procreative, i.e. the way humans reproduce.
By way of contrast (ye cats, it's repugnant to write this way, but here goes): putting your semen in a warmed Mason jar is NOT "procreative sex," even if your wife scooped it right up with a turkey baster and got pregnant with it. It lacks the fully human form of the sexual embrace that it ought to have. It lacks the kind of union that makes things right.