It is possible that their QA involves checking whether an app uses prohibited API or whether it crashes the system or hogs memory etc. It is obviously a high level QA. Just search and see how many "task killer" apps available on Android device.

Also, I think if this app-review process is not beneficial to users, I dont think they would have started this in the first place. Sure, it is an issue to thousands of developers, but it is beneficial to millions of users.

Business related motives could be a big reason as well. But, who is not?