What's neat to consider here though is, even though the PKGs are ran in game/user mode, it essentially puts our foot in the door, possibly allowing us to elevate privileges. With Geo's exploit, we were only able to "peek" at privileged HW functions, and not necessarily modify them in any useful way. For a simpler explanation, think of it like this:
With Geo's exploit, we're bank robbers standing in front of a teller telling them to give us the money. We still have to rely on the teller to retrieve the money, and they could easily be pushing the silent alarm button while we wait. We only have access to limited funds.
With the Jailbreak, we're in the bank after hours, at the vault door. While we're not technically "in the money" yet, we're close enough now where we can start to work our way through the door and have access to almost unlimited funds. As we're not having to deal with a middle man of sorts, we can throw everything at the door until the hinges finally break.
The ultimate goal? To get ahold of the bank manager's code (the systems's encryption keys) and voila, we're rich, biatch! While this last step may still prove to be nigh impossible, our chances of running exploits as unsigned code and elevating our privileges to "bank manager" status are greater than just poking at the memory registers or gleaming data from the SPEs.