...the results are better than the source.. Is that possible?
No.
You are being fooled. YouTube encodes all video at 320x240 but displays them at 450x370 on their web pages. This causes jagginess and blockiness due to upsampling errors, which are particularly noticeable since the upsampling is an uneven multiple of pixels. A video file always looks better at its native resolution, so even if you re-encode (which always causes picture degradation) but play it back at the native size, it will look better than the original encoding at the wrong size.
I examined the files in detail and the re-encodes are all worse than the original. If you want to compare codecs, compare a frame with motion instead of a still like the screenshots. Stills are easy to encode, but even slight differences in codec quality are obvious during rapid motion scenes.