[jhowell]

Amazon normally does not make minor updates, such as fixing typos, available to existing customers. The option to update is only made available if a substantial problem is fixed, although major publishers are allowed to break this rule. This likely reduces Amazon’s customer support effort (and cost) related to book updates.

(Added: It might not be obvious, but trying to maintain the current reading position, highlights, and annotations when the underlying content has been replaced is a difficult problem and Amazon is not always successful at it.)