[RPG] Does Improved Grapple Increase CMD against escape

I strongly disagree with Phill.Zit's reading here. Your own quote says it all:

the weapon’s bonuses apply to the roll.

It goes on to clarify ('therefore…') this would require a finesse weapon. But bows use Dex as their bonus despite not being finesse weapons, so should use Dex for these checks.

In fact, I'll go further and say you have to use Dex. Finesse weapons give you the choice, whereas bows do not.

And note the wording on the types of combat maneuvers it applies to. Normally with a bull-rush or grapple

you're [not] actually using a weapon

so you'd be forced to use Str. But again, here you are using a bow so must use Dex.

Reading the rules in a strictly literal sense, I don't think it actually counts anything as a true grapple.

1. Make a ranged attack against a foe that has something you can pin (clothes, armour, bags) and something to pin it to (nearby perpendicular surface).
2. If you hit, you roll an opposed grapple check. Yes, while this uses the rules from grappling, it does not specify anywhere that you or the target are considered to be in a grapple.
3. There is no required opposed grapple roll for the opponent to escape, they simply DC15 Strength or Escape to break free.

I think the only reason you make a 'grapple' check at all is to include all relevant size/skill factors. A Huge creature's arrows would basically be the size of a javelin to a small creature, so it stands to reason that bigger projectiles pin more successfully than smaller projectiles.

It doesn't specify that you or your opponent are considered to be in a grapple, nor does it specify that normal grapple damage applies (or constrict damage for that matter). It simply requires you to make a roll that uses all relevant bonuses for grappling in terms of size and strength.