From the screen survey carried out by MediaPortal Team only 1 year ago, 33% of users had a resolution of 1920x1080. That means 67% of users do not use this resolution. The largest majority was 1280x720 + 1366x768 at about 36% (I've lumped these together as they are almost identical and split the vote unnecessarily when comparing 'HD Ready' vs 'Full HD').
By creating textures suitable for a 1920x1080 skin you are putting higher workload on HTPCs for the vast majority of users as they have to store larger textures that then need to be downscaled - all using extra resources on the machine whilst MediaPortal is running. Also, if the skin is developed for 1920x1080 then perhaps this will look very cluttered downscaled to 1280x1720 etc.
By creating textures suitable for a 1920x1080 skin you are putting higher workload on HTPCs for the vast majority of users as they have to store larger textures that then need to be downscaled - all using extra resources on the machine whilst MediaPortal is running. Also, if the skin is developed for 1920x1080 then perhaps this will look very cluttered downscaled to 1280x1720 etc.