I would guess most peoples issues with Wireless N are that the router and device are on separate floors or have multiple walls between them. Apartments could potentially always have issues due to interference. With a clear signal N is perfectly capable of streaming Blu-rays. None of my HTPCs are currently wired and I haven't had any issues with playback. I wouldn't think AC would help with this at all since the penetration won't be as good as N. Clear signal multiple streams obviously AC will be a clear winner. N is definitely going to choke with multiple streams or other heavy local traffic. Another thought is that people who are upgrading to AC and finding a vast improvement to their streaming should also factor in that the AC devices available are typically going to be much higher quality devices than what they most likely upgraded from. Getting a top of the line N access point and card could provide you great improvement as well.
Running Windows Home Server 2011 Evil Abandoned Edition