Someone made a point elsewhere that was actually depressingly logical; in the case of folks who might be inclined to buy both consoles during their lifespan, they might be more inclined (assuming they only decide to pay for one subscription) to pay for Xbox Live Gold instead of PS+, under the idea that more of the Playstation 4's features don't hinge on paying that cost. I.e. if you can already use DVR, Netflix, Internet Explorer, etc, etc, etc on the PS4 for no sub, and not on Xbox One, as a multiplat owner you're more likely to just invest in Xbox Live Gold, because teeechnically you get More Bang For Your Buck, even if it's largely because most of the Bang is locked behind the paywall.
It won't really apply to me; though I might get an Xbox One in a couple of years, it's going to be my exclusive-only platform, and I won't really be doing much online gaming on it, not enough to bother paying the sub at least. But I can imagine that folks who own both consoles, on measuring what the sub 'gives' them, could very well end up giving Microsoft the lion's share of the money in the long run, which means the miserly approach would actually turn out to be the financially crafty approach.
That being said, I don't know the numbers in terms of how many people owned both console this generation, even, so I couldn't say whether it would really make a difference in the long run. Of even that number, in many cases it probably would still just come down to which was the Exclusives-Only platform, and which was the preferred multiplat system.
It also hinges upon Microsoft's evident expectation that the policy wouldn't lose them a number of console and software sales that offset that benefit which, considering the atmosphere still seems a bit, er, charged, could backfire if enough prior Xbox owners have jumped the proverbial ship.
...anybody else find the economics and social behavior surrounding the console launches slightly more interesting than the consoles themselves? xP