@clacke I think that this is convenient to have both Beta and Production versions of an application via the same channel, without a need to reinstall the application in order to switch from Beta to Production and vice versa.
Regarding delay of some hours: My understanding is that Google, the same way as Microsoft and other software distributors with billions of customers, deliberately introduces random delays of new versions / updates availability for download. I mean, subscribers receive notifications about application update randomly during some period of time. This allows to spread a load on "Play Market" servers and avoid outages. For ubiquitous and large applications like Windows this spread is even several weeks AFAIK...