Obviously it's simple enough to change a storage engine if you are not using InnoDB for something after an upgrade adds a table, but I was just thinking about what would happen if someone was using some of the more advanced storage engines for tables. Like if someone was using MySQL Cluster (where all nodes are a valid master), you would be using the NDB storage engine. Creating an InnoDB table within a MySQL Cluster would be bad because it's not going to propagate it to other nodes (since it's InnoDB, it would only exist locally on the one node). So queries to a new InnoDB table are going to fail unless they happen to be hitting the same node it was created on. Or maybe someone just can't use InnoDB for whatever reason (screwy DB server config or something), they could simply override their storage engine to MyISAM or something... or maybe someone wants to use the Aria storage engine... anyway, you get the point.