I would recommend that this be added to the BBFAQ under General WiFi info or something like that as I am probably not the only person that wants to understand this.
I found this on another site and confirmed it with the information on BlackBerry's support site. This explanation seemed more concise to me so I am leaving it here.
I found it interesting that the only time the HotSpot Browser is needed is for raw local content when the device cannot connect to carrier. I know, what the #$#% does that mean....then I realized that means that the only time the HotSpot browser is required is to connect to the HotSpots authorization page in order to accept the terms and conditions and/or sign in. Once authenticated you can switch over to the Internet or BlackBerry Browser for increased speeds.
If you want to see the BB support wording to clarify or confirm it is here: BlackBerry Search Results
"I would like to clarify the differences between the Wi-Fi Browser, BlackBerry Browser and Internet Browser. The Wi-Fi browser provides a direct connection to the Internet with no compression or optimization, it is a "raw" connection to the Internet. It does not utilize the carrier's infrastructure or BES (MDS) in serving web pages. For BES users when connected to a Wi-Fi network, the BlackBerry browser will utilize the Wi-Fi connection back to the user's BES (MDS) for optimization, compression and encryption. For BIS users, the Internet Browser will also use the Wi-Fi connection back to the carrier's infrastructure for optimization and compression. Thus to get a more optimized browsing experience, BES users might want to use BlackBerry browser and BIS users might want to use the Internet Browser."