Well monitors it is tougher cause you never know how they measure their contrast ratio, grey to grey scale and so on. 1 monitor can have a 6,000:1 contrast ratio but actually be worse than a monitor that says it is only 3000:1 due to how each company interprets the contrast ratio facts.
This also is tough to do considering the wide amount of monitors out there, different screen sizes, different screen resolutions and so on. There is no way for us to write up a clear cut guide on which monitors are the best when there is no way we have physically used them all or cant test them all accurately.
With power supplies it isnt that hard. There are more places that have done reviews, tests and benchmarks with them. Monitors it is hit or miss if you can even find a review about the product let alone get some real information about what the product offers. I mean screen shots are pointless cause you are viewing them on your monitor so you wont see what they see.
Then comes in response times. Some people can live with 5ms just fine. Others swear by 2ms. Some dont even go that low and live with 8ms or more. So as you see there is so much more to take into account when it comes to monitors than it does for PSU's as those you just need power requirements and amount of rails basically. With monitors you have to have so much more information about what the end user wants and likes that it is impossible to write up a cover all guide for everyone.