Every week I see how other players obtain items at the ends of the games. For example, parts of armor sets. I have played many hours of Counter Strike Go and in that game the loot refreshes every week. But I don't know if this system is the same in Dota 2.

3 Answers

In Dota 2 there is an Item drop system:

The item drop system is a feature that allows players to obtain cosmetic items for free through playing the game.

Notes:

• After every matchmaking game, each player has a small chance to receive an item or set.
• All drops in Dota 2 are solely based on time played in Dota 2 via matchmaking.
• Winning, losing, or individual performance has no effect on item drop chance.

And also:

While spectating a tournament game with over 100 viewers, one or more Heroic items are randomly given out to viewers each time a memorable event occurs.

For more information about Item drop system read this.

2

From my personal experience, I can say that there is no loot refresh system in Dota 2. The stuff is awarded randomly. Last week I've got like 2 pieces of different item sets and of different quality, but haven't got any items at all for like half a year or so.

The exact chance of getting an item at the end of the game was not disclosed by Valve but they stated:

All drops in Dota 2 are solely based on time played in Dota 2 via matchmaking.

So I guess the longer the match, the higher the chances of getting an item (something I did notice after very long games, having an increase on the number of players that usually receives items)

One thing I have noticed is that the chance is purely random and not RNG as most of the in-game chances (it does not increase if there are multiple games without receiving)