It's a non-standard (NoSQL) database. Even SQL databases, despite years of standardization and efforts at poaching each other's customers, still have rough edg

It's a non-standard (NoSQL) database. Even SQL databases, despite years of standardization and efforts at poaching each other's customers, still have rough edges that make moving between different SQL database products non-trivial. Just because you can get your data out doesn't mean you're not locked in to all of SimpleDB/DynamoDB's quirks, of which there will be a lot more because it's not following a standard approach. Your code will have to go through contortions to work around / adapt to the SimpleDB limitations; effort which might well be wasted or counter-productive on a different system. That's the lock-in with AWS in general: API lock-in, not data format lock-in.