For me, it's not so much the immediacy of the updates but knowing that I'll get more than the one or two that Android vendors typically provide before abandoning a product. Eventually Android will advance to the point that the N4's hardware can't handle it without the user experience suffering, and when that happens, Google won't push any more to it. But I don't see that happening for at least two years, based on the headroom in the N4's processor and memory.
In fact, the older that the N4 gets, the more I'm going to wait before installing an update so I can see if other owners are reporting problems. I leaned that the hard way with the iPad 1, which I should have left at 4.x instead of upgrading to 5.x, whose features don't outweigh the performance hit. Just because Google, MSFT, Apple, et al say that a device can handle something doesn't mean it can handle it without the strain showing.