I was confused too. However, I think they are going to bring in-app search (like Android) to iOS. They can always auto index the apps on the device and then send the data to their servers. Alternatively they may also relase APIs for developers to push user specific content to their servers to index items (more like ElasticSearch or AWS CloudSearch.)

$200M is a lot of money to just improve the app store search. They might end up using it for that too.