Yes, this website have made developers aware that 4:3 isn't acceptable for 16:10 users.
There is nothing wrong with 4:3 on a 16:10 display if that is all the game can reasonably support. The WSGF favors the support for the wider aspect ratios because of the whole championing widescreen thing. :)
But what about 16:9 being supplemented for 16:10? Why is this given a pass when we are getting less height and reduced width when a game is running 16:10?
You can't get both at the same time. You get less display height when the game uses letterboxes to keep the wider aspect ratio and you get reduced width when the game uses a narrower aspect ratio.
I think you are describing a game with a 16:9 baseline that uses a fixed horizontal fov so that narrower aspect ratios get more added to top and bottom of the viewable area. That is generally undesirable behavior for a multitude of reasons which have been mentioned throughout the site.
For example, Dragon Age, where if you toggle between the 2 aspect ratios you get the same height but only get increase in width using 16:9. That's not the correct aspect ratio if you want to use 16:10 yet it's not brought up or discussed.
It is the correct aspect ratio if the game supports a 16:10 aspect ratio, which it does. Dragon Age is not using the 16:9 aspect ratio for a 16:10 resolution, it is using a 16:10 aspect ratio. Just like it is using a 5:4 aspect ratio for a 5:4 resolution.
It may have been made with a certain aspect ratio in mind but it has been designed to support aspect ratios as narrow as 5:4. With each wider aspect ratio more is added to the sides of the viewable area. But the game has been designed to run in a 5:4 aspect ratio.