burkhartmj :
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I have only limited knowledge of this, but firstly, TN is a known 'bad' technology. Even if people don't know how or why it's bad, a lot still have heard it is. Not that I necessarily agree, but I also own 2 Dell Ultrasharp monitors because I care for myself. Secondly, I would imagine with most smartphones using IPS that there is an economies of scale in manufacturing that makes TN less cost effective. Don't that for certain, but it wouldn't surprise me.
I'd say another major reason that pixel increase only goes past 1200p in IPS forms is because people who wouldn't notice the difference between TN and IPS would GENERALLY not notice the difference between a 24-27 inch monitor being 1080p or 1440p, because they mostly watch content that maxes at 1080p and aren't as concerned with insane detail in games. There are always exceptions to this [as you very well might be], but it wouldn't be a large market.
I think most people can tell the difference between an IPS and TN monitor, but since responsiveness (through reduced input lag and reduced response times and increased refresh rates) hasn't historically been an aim of IPS monitor manufacturers, to me, TN monitors and IPS monitors are clearly built for different purposes.
Also, for me, it's not about insane detail but rather the ability to see more of what's going on on a single panel when it comes to gaming. As a matter of fact, I'd like the same level of detail, but the ability to see more on a single panel.
Another question I've often pondered is I know most people's HDTVs (whether LCD, LED, or LCD/LED) don't use IPS technology, so why can I view them from just about any angle without much color or image distortion at all, but go at a PC from an angle and the TN monitor lets you know?