Did you mean to reply off-list? I assume it was Gmail again :-)
Of course concessions must be made to produce a practical system. Does your semver allow 1.0 in addition to 1.0.0?
The SemanticVersion in distlib is currently strict and doesn't allow x.y, but the test script which produced those results did a simplistic check for matching x.y and tacked on a .0 in that case, before deciding on a pass/fail for semver.
Really what we hope to gain is a good way to order pre and post releases having the same major-minor-patch.
The "legacy" scheme (setuptools/distribute) will do that, won't it? (For some value of "good", of course.) Of course it has drawbacks, as mentioned in PEP 386: it doesn't constrain version numbers to follow a sensible scheme. Of course, to enforce any additional constraints would need PyPI metadata checks to be added, which would no doubt annoy the minority of people who name their versions like "02 Jun 2010", "pre-release", "0.1.5dev-20111031", or "0.5.0-protobuf-2.4".