Yep .. isnt there a way to watch older replays ? A replay viewer or smth like that ?
Yeah, there's a couple of ways. There's a link in my signature below. The catch is that it's only useful if the multiplayer isn't changed, and the last patch changed plenty (there have been a number of minor patches in the past that made replays old while only changing minor singleplayer stuff).
All the rules for how units act are provided by the game itself. The replays files only contain movement and attack instructions for that game. When the rules change, those instructions stop making sense, unfortunately.