If you compare The Argentinian Attack in the Pirc (f3, Be3, Qd2, o-o-o) with the Sämisch Variation, the pawn on c4 is in many variations a weakness, which also costs an important tempo.

The pawn on c4 is definitely helpful as it aids in stopping both d5 and possibly attacking blasting open the queenside by pushing the a and b-pawns. I don't even think Black should have to worry about theory when playing against the Pirc g3 system.

I think only Caissa herself knows the answer to this question ...

Generally speaking, the pawn on c4 means White has more space and central control in the KID than in the Pirc.  This is especially important in lines where Black plays ...e7-e5 and White closes the centre with d4-d5.  In the Pirc White will sometimes end up wasting time moving his knight on c3 before pushing his c-pawn.  Meanwhile, Black's attack on the other side of the board rumbles on ...

On the other hand, having c2-c4 in means the d4 square is more of a weakness, as White can never defend it with c2-c3.

The pawn also gets a bit in the way of the light-squared bishop. The moves Bf1-c4 and Bf1-b5 crop up sometimes in the Pirc.  In fact, in the some of the main lines, establishing a bishop on the a2-g8 diagonal is a definite goal for White. The option of responding to ...Nc6 with Bb5 is a common way of fighting for control of the centre, especially in the Modern.  Naturally, these moves are rather less common in the King's Indian!

Last but not least, c2-c4 takes up a move which could be used to develop a piece!  The most obvious contrast, in my view, comes from a compariaon between the Four Pawns' Attack in the KID and the Austrian Attack in the Pirc.

After 1.e4 d6 2.d4 Nf6 3.Nc3 g6 4.f4 Bg7 5.Nf3 Black can play 5...c5 but it can get razor sharp after 6.Bb5+ (clearly not an option in the KID) 6...Bd7 7.e5!?.  But after 1.d4 Nf6 2.c4 g6 3.Nc3 Bg7 4.e4 d6 5.f4 0-0 6.Nf3 c5 is seen as a very reliable move.  This is not to say that White can't try for an advantage in the Four Pawns or that the play doesn't get sharp sometimes - just that it is not quite so knife-edge as the line of the Austrian I have referred to.  The main reason for this, is that White is further ahead with his development in the Austrian Attack.

Really though, it is a case of swings and roundabouts, and it is largely a matter of taste - for both sides.

In a sense it is similar to the debate in (eg) the Kan Sicilian (1.e4 c5 2.Nf3 e6 3.d4 cxd4 4.Nxd4 a6) when White has the option of going for a Maroczy Bind setup with (eg) 5.Bd3 Qc7 6.0-0 Nf6 7.Qe2 d6 8.c4, or of developing 'normally' with 5.Nc3 etc.  Both approaches have their fans, but I don't think anybody can really say that one is objectively stronger than the other.

In these King fianchetto openings, does white benefit from the pawn on c4?  I was thinking: does white have more of an advantage in a Pirc/Modern or in the KID?  At this stage, I'm unable to decipher what the potential differences could be to benefit or hurt white. 

Perhaps white could try d4 Nf6 Nf3 g6 Nc3!? and attempt to transpose back into Pirc lines...(of course one should know the opponent is a KID player, otherwise Nf3 may not be as good as allowing a Nimzo/QID.)

Any thoughts?

NeX iRae