Isn't TN very similar to IPS? They are both types of TFT LCD's. I did some research recently, as I've just bought a new monitor.
This is what I read. It also states that IPS displays are plagued by slow response times.
IPS isn't always better :
I'd imagine the monitor in question is going to be the higher end of TN panels, Which would make it better than half the IPS screens, and probably cheaper than them too. The article is rather old now though, and probably wrong as of now, I don't know, others may know better than me.
A simple conclusion would be :
IPS - Photographers/Photoshopers. e.t.c - better colour and quality - slow response
TN - Gamers and general use, not so great colour, brilliant response times, allot cheaper.