Well I don't know if I would call it complicated. It depends on what socket libraries are available. Personally I use Oxygene for Java so that is quite easy, but I haven't used FPC or Delphi in a long time, so I don't know what kind of support they have.
Yes it is possible to use readln and writeln. As I see it, it really depends on what sort of data you want to send and how good a socket library you have available. But I suppose it would be nice debug feature, if a bots console output could be shown during testing. In the end, it depends on who is making the game and what that person prefers. IMO that person would also have to provide a template for each pascal dialect, so that contestants don't have to write the functions for communication with the server, but they only have to focus on writing the ai. Ideally the would only need to implement one method:
Code:
procedure TBot.DoMove(FGame: TGameMetrics);
begin
...
SendCommand(...);
end;