javascript - 关于nzakas对const和let解释的一点疑问

先附上nzakas的讲解地址：
https://github.com/nzakas/understandinges6/blob/master/manuscript/01-Block-Bindings.md
在zakas对let的讲解中举的例子：

var funcs = [];
for (let i = 0; i < 10; i++) {
    funcs.push(function() {
        console.log(i);
    });
}

funcs.forEach(function(func) {
    func();     // outputs 0, then 1, then 2, up to 9
})

其解释为
1.On each iteration, the loop creates a new variable and initializes it to the value of the variable with the same name from the previous iteration.

2.The let declaration creates a new variable i each time through the loop, so each function created inside the loop gets its own copy of i. Each copy of i has the value it was assigned at the beginning of the loop iteration in which it was created

这意味着每次迭代，都会重新用let声明i，赋值，并且产生一个新的块级域，我这样理解对不对呢？是否等价于{let i = 0;...}{let i = 1;...}...{let i = 9;...}分为10个块级域，而且每个i都处在不同块级域之中呢？
但是同为块级域的const：

var funcs = [];
// throws an error after one iteration
for (const i = 0; i < 10; i++) {
funcs.push(function() {
    console.log(i);
});
}

为什么不会在每次迭代中重新声明赋值并且产生新的块级域呢？像{const i = 0;...}{const i = 1;...}...{const i = 9;...}这样呢？这是否说明const和let在for迭代中的行为不同呢？
然而，在for-in和for-of循环之中，为什么let与const又是相同的？

var funcs = [],
object = {
    a: true,
    b: true,
    c: true
};

// doesn't cause an error
for (const key in object) {
funcs.push(function() {
    console.log(key);
});
}

funcs.forEach(function(func) {
func();     // outputs "a", then "b", then "c"
});

其解释为The for-in and for-of loops work with const because the loop initializer creates a new binding on each iteration through the loop rather than attempting to modify the value of an existing binding
这里有一些不解，每次产生新绑定和在现有绑定上修改之间有什么区别吗？for-in循环不是将属性名赋值给变量吗？为什么是产生绑定了？每迭代一次key的值不都变了吗？为什么仍然能够工作呢？
刚学ES6，对以上实在有些不解，还望大神解答！