If it's technically impossible to set it above 1080p, even if Platinum has tested such resolutions, there's going to be some disappointed folk. Sorry, Platinum and co. First time PC build and all that, but that's just how this stuff rolls, justified or not.
I don't play above 1080p, but higher resolutions are great for supersampling. I do wonder if JP just means they've not tested/supported anything above, or if it's technically locked. If the latter, won't be surprised if the cap is broken. Usually happens.
Just use SSAA or SGSSAA.