vcd-svcd bitrates same: video looking different :|

ok.. so i encoded a piece of video in a standard svcd and then i encoded the same piece of video into a non-standard VCD that has all the same bitrates, i play them both back and compare.. but the vcd still looks like it did as a standard vcd :/ and the svcd looks good... but what i can't figure out is how would they look that much different if they were encoded at the same bitrate. IS it possibly the VCD and SVCD encoding standards that are different? like some different ways of encoding methods in vcd and svcd are different?_X_X_X_X_X_[small]uggh[/small]