I feel like this should be an imminent update but may come later than it should. The 75x75 avatars look awful, especially on a Retina Display. We should at least be allowed 300x300 minimum.
The reason normal resolution images look awful on Hi-DPI displays is because companies made the wrong decision about how to handle them.
They're resampling the regular images (bilinear/bicubic/etc) instead of resizing them (nearest neighbor).
I know a lot of people are going to say that nearest-neighbor interpolation is no good, however we are speaking about a single, fixed case here: making low-resolution images bigger at a perfect multiple of 2.
This is what's happening and why Apple and everyone else are right when displaying Retina images on regular displays and wrong when displaying normal images on Retina displays.
I used the MacRumors logo since Arn has done a good job with his Retina logo (500x142 pixels PNG displayed at 250x71 pixels).