As jaguar and wa1 said in the post you linked to, sometimes it may not work which proves my point. Also compatibility has nothing to do with performance. 2.0 x8 is the same as 1.0 x16. Even high end cards such as the 570 and 6950 only show a 2-5% decrease which is unnoticeable in actual gameplay as it only equates to 1 or a fraction of a fps. http://www.tomshardware.com/reviews/pci-express-scaling-p67-chipset-gaming-performance,2887-9.html
The lower end cards will show no change at all.
I've helped plenty of people where 2.1 doesn't work and I've helped plenty of people where it does work. Yes it's true it's a minority but it still happens.