What the statistic completely ignores is that the £394 a year spent on tech is almost certainly spent on one or two big items. I'd say iPhone ownership is fairly ubiquitous - the average cost of an iPhone is probably about £360/year. The rest is probably made up of the fraction of a tablet or laptop that the average woman purchases each year. Even if someone theoretically spend £394 a yer on tech, it doesn't mean that advertising a tech product to them will make them buy it. Phone purchasing decisions happen annually, laptops or tablets even less frequently. Cosmetics, on the other hand, are purchased across many small transactions in a much more continuous manner, giving far more scope for effective advertising return.

And as others in the comments have said, magazines are really about delivering adverts to customers.