an application that runs on a distributed computing system
Unfortunately this is just not a very good definition. By this definition, Facebook is a dapp, because it also runs on distributed computers. There is not just one server running the Facebook app, but many servers, likely front end applications, API's and database servers all working together to run the application.
IMO a narrower definition captures the essential idea of a dApp, which is an application where the outcome is determined by a decentralized consensus system. In that case peakd and hive.blog would not be dApps on their own, but clients of a greater dApp - Hive itself being the dApp because they all share the same application logic of the native Hive smart contracts.