From what I gather, the general contract of the Collection and DB API methods is:

• DB.command() will return a CommandResult to the user who then take responsibility to check ok() or throwOnError() as they wish.
• The "helper" methods that wrap commands, e.g., distinct() call throwOnError for the user automatically.

However from what I see there are several "helpers" that do not, making the pattern sort of inconsistent for users. The examples that I was able to find where throwOnError() is not called:

• DB.getStats()
• Mongo.fsync()
• Mongo.fsyncAndLock()
• DBCollection.aggregate() returning an AggregationOutput