Many airlines have changed the baggage allowance within the past year; for example AA changed the piece system to 50lbs per piece (instead of 70) but had to back off after a few months. I have heard of several tickets to the US which were on weight instead of piece; I don't know why (just as I don't know why the US had a piece system in the past). So it seems that you have to check the baggage allowance as part of the fare rules these days, if you care (20 kg is plenty for a RTW trip, even one including winter/summer weather, most of the time I travel with less despite having a 60kg+ allowance). It sounds like the LH/NZ "special" is really sold as 2 or 3 separate tickets with the NUE-SIN leg being a separate ticket from the rest.