d6 or 0-0?

There are two positions to consider which one of the two moves above to play. 

King's Indian Defence:

Why is d6 more popular than 0-0? If the point is to avoid 5.e5, then Fischer have shown that 0-0 5. e5 is better for Black. What is White's strongest reply to 4...0-0 (besides Nf3 which transposes to the mainline) that takes advantage of the delay of d6?

I think 0-0 even has the advantage of tempting White to play the poor move 5.e5

Ruy Lopez

Both of the moves usually played after each other, but 0-0 first has an advantage of playing the Marshall Gambit. So why do most people play 7...d6 first? What is its advantage? And how to take advantage of 0-0 besides playing c3 which transposes to the main line (while also allowing Marshall Gambit)?

0-0 often leads to the same positions as d6 but 0-0 is more provocative and tempts white to play e5 but can cause he or she overextended. Fischer played 0-0

O-O can't be wrong (except few cases where O-O is really a suicide). 

In the Ruy after 7...0-0 White has the choice of playing an Anti-Marshall system with 8.a4 or 8.h3. The likes of Kasparov and Michael Adams have played this with some regularity.

There are several cases where O-O is just wrong. This happens mainly in French Defense as shown below. 

As my personal choice, I play ...d6 first in the KID as a waiting move to be sure my opponent does not get me out of my repertoire if he plays Bg5 (in such case, I am not supposed to have castled kingside).

In my case, it is a matter of transposition.

Here the study game so you see my point:

Erratum: 7.Qa5 is usually played before 8.g5. I don't know how to edit the move order in the diagram. My bad.

If you all say that 0-0 can't be bad in the lines I mentioned, why d6 is more popular? That's what I'm asking, guys.

And also, pfren, 4...0-0 5.e5 White scores very low, maybe due to the famous game by Fischer. Maybe it's not that bad, but it gives me the impression that 5.e5 is not too good. Most people play 5.Nf3 to get back to the main line.

I think this is a matter of trend. For example, O-O is the most popular move in many variations such as 1. d4 Nf6 2. c4 e6 3. Nc3 Bb5 4. e3 O-O Nimzo-Indian whereas the major alternative is 4. ... c5. I believe nobody can explain why O-O is the main move in some of these variations and not in the others. I see O-O as a lazy way to play, if you forget the theory, just play O-O and you will be okay 99%.

I play 4... d6, and it's mostly because I've been burnt in the past waiting too long to push the pawn, and so now I do it ASAP.

So, I conclude that d6 is played because in some lines Black is not castling short. 

Get it!

How about the Spanish?

I mean, What about Ruy Lopez when black faces the option either 7...d6 or 7...0-0?

0-0 has the advantage of playing the Marshall Attack. So what's its disadvantage?

(I haven't grew up yet, I'm only 15, and I didn't know exactly where in this thread we discussed about castling queenside.)

If no one wants to play the Marshall, then it would not be this popular.

and one more

clearly that's not what you originally said nor meant. enjoy the games - very strong players in all of them.

"no one" means "no one." i'm not interested in arguing with you about it. you made a claim that was not true and there's really nothing more to it. have a good one. 

Please don't fight in this forum. I don't even intended to discuss where to castle ._.

It's amazing how some people are incapable admitting they were wrong, and move on. Castling queenside is  a viable idea in the Ruy Lopez. It's a fact, the end, next.