All players must have the same version of the game. Should you not, you will be informed about the fact.
Having cross-version compatibility (especially forward compatibility) would be much more trouble than anyone can wish for.
Similar goes for replays - since these are more or less reproductions of what buttons have been pressed and at what times, the game has to match up for them to reliably produce the same result on screen.
All publicly released versions will remain available for download for this reason.