Here's the relevant extract from a Partner Portal support case that went on about this topic for a LONG time:
I have been working through this and was able to reproduce the behavior in an internal environment and came to the realization that the particular limit tracking appears to be: Matching DmlEvent X number of subscribers.
I have been assuming all along that the limit is in fact just the Matching DmlEvent event. The current behavior says the limit tracking is otherwise.
In your case, I believe that the probable reason for the increased multiplier even when just testing via the vf page, is that on refresh, close etc.. the unsubscribe code you have is not completing/running properly.
I will have to check with R&D on exactly how that limit is supposed to be tracked/calculated. From there, we should know exactly where to focus.
and then in the next exchange:
I received confirmation that the limit is calculated based on [Matching DmlEvent X number of subscribers].
So evidently the stream API limit "Maximum number of events per day (24–hour period)" is more accurately defined as "Maximum number of subscriber-directed events per day (24-hour period)".