alt Hacker NewsVector clocks are certainly cool but fundamentally premised on the idea of having multiple 'live' versions of a value at once. Amazon's original Dynamo paper required conflict resolution at the application level, which is a very strange framework to build applications on. (Notably DynamoDB has moved away from this, I believe to Last Write Wins.) Cassandra takes the latter approach by default as well, I believe.
yes there's that idiosyncrasy, as well as client ideally needing to read the previous clock from the DB before writing an update for that key unless it's ok with the write being viewed as concurrent. Plus the extra memory overhead to store the clocks in the client.