The biggest factor for me, besides the controls, is not the graphics per se. It's the immersion you get from peering into a very highly detailed scene on a monitor that fills your field of vision. You simply don't get that on the sofa, no matter how big your TV is. Shooters are first person. In other words played from your point of view. You need to be immersed in the world you're playing in, not sat on the sofa, detached from what's going on. Even a hundred inch screen at a normal distance from a sofa would not fill your filed of view like a proper monitor, and even if it did, you'd be peering into muddy 720p graphics, with screen tears and very little or no anti-aliasing.
Yes. One pays the price for the benefits that a proper PC setup offers (and yes there are also negatives) but then we all spend our money on what we like.
That's possibly the most sensible sentance I've ever seen you post on here....