My take on this is that Paizo wants there to be an in-game incentive to encourage Gunslingers to play to the daring, risk-taking glory-hound concept of the class.
My roommate and I are going to be playtesting this class very soon, and we're planning to incorporate a suggestion made in the thread you quoted that passage from:
'Rixx wrote:
I think it ties in with a "daring act" - shoot at the head honcho even if you're surrounded by his cronies, attempt to wrestle someone to the ground, dash by a bunch of monsters so you can get into position for that perfect shot. Doing something risky knowing that you could get smacked down for it is worthy of grit.
In that post, 'Rixx was talking specifically about regenerating Grit by provoking AoOs, but the roommate and I don't really see a need to be that specific since such acts already fall nicely within the "Daring Act" optional rules. Basically we're planning on giving the gunslinger Wis Bonus + 1/2 Level starting grit, and taking out all regen except performing "daring deeds," with the GM having final say on whether a deed was badass enough or not. We'll see how it plays out.
Hopefully, providing a little more of a grit pool - with a "take big risks, get some Grit back" mechanic still in place to encourage playing to the concept - will encourage using Deeds more often, and give the 'Slinger a reason to do more than just the boring "get in close range and full attack rinse repeat" tactic others have described.