Screenshot of en.wikipedia.org on iPad 3 with Retina display
Wikipedia's and the other projects' logos are low-resolution raster images, and appear visibly pixelated on high-resolution displays such as on the third-generation iPad with Retina display.
Fixing this will require redoing a loooot of custom logos. :)
Recommend using either SVG forms (need PNG fallback, needs to be maintained) or defining 'low' and 'high' resolution logos (which then have to be maintained). May be icky.