I think it is a ratio of good to bad. Take Drive train systems. The different between xt and xtr is almost purely weight. Not a concern for me. But price is. A rear derailuer (sp) costs 90$ - 200$ respectively. I would never ever think of buying the xtr. Too expensive for something I don't care about. I am not a gram counter and never will be. Hell I weight 250
.
I go through the same process with everything and find the best deal to fit my situation. Because of my torquing power and the style of riding I do I spend a log of money in three area. Rear hub, bb and pedals.