(This is more or less a meta SX question - but I haven't found an answer there.)
The question says it all, and the answer seems to be "No.".
For the planned Sybase-hosted SQLA site, I would suggest to turn the answer into "Yes" (if the underlying OSQA software does allow for this feature), and would even suggest that comments can be upvoted and downvoted like answers.
This site shows that comments are very helpful:
They often turn out to be real answers (but were possibly written as comments because the commentator wasn't sure if they were appropriate or correct), or they might give relevant hints or add further value to existing answers.
IMHO, that should be honoured - at least as long as reputation is necessary for certain priviledges.
This question is marked "community wiki".