"Hardware textures compression support was not detected. This video card feature is required to run the game.", same one as you. Working around that error just gives me grey screens in-game, apart from the UI.
I have wine 1.3.8 as well, didn't use winetricks for d3dx9, instead just copied the d3dx9_36.dll to the lotro directory, which worked perfectly with the proprietary ATI driver.
Didn't get anything from xorg-edgers. Someone on the IRC channel told me texture compression is simply not yet supported by libtxc_dxtn for r600 cards and above. Seeing as I have an ATI HD 4870, which is a r700 (I think), this situation is hopeless for me I guess. I'll just have to stick with the proprietary one and try to get my performance up.
This makes sense. Although, I'm not sure if libtxc_dxtn is not an abandoned project.
Also, I think this is a good description of the situation with S3TC and MESA http://dri.freedesktop.org/wiki/S3TC