Then why not recommend a Mars II in that case? Or the GTX 590?
The point being, just because you don't have a budget doesn't mean you buy something that is 10 percent more powerful for 1.75 times the cost. The only way I'd ever recommend a GTX 580 is if you need the 3GB version for extremely high resolutions. Just my opinion, I don't like spend other people's money, however.
If budget is of no concern, I like to recommend the fastest single core graphics card available at the time of purchase. This allows for the most resale value in the future and possible "future proofing", if you believe that even exists.
I completely understand where you are coming from, there is absolutely no point in a GTX 580 over a GTX 570 from a price to performance ratio. But I implore you to look at it from a different point of view, some people just want the best that their money can buy. In this case, the best single core graphics card out there is the GTX 580; sure it may be unreasonably expensive and most would consider it a waste of money, but some people are willing to pay that premium for the few extra frames.
Lastly, I don't know why you keep saying that we like to spend other people's money. I am simply offering my advice and supporting it with a personal opinion. I am in no way forcing another person to spend more money then necessary.