The order of birds on world lists usually aims to reflect the relatedness of the different groups, so that groups that are more closely related are put near each other on the list. This is the reason that, for example, swifts and swallows are a long way apart on the list.
Our understanding of these relationships has been changing rapidly in recent years because we have learnt more about relationships from DNA analysis. Because birds diversified very rapidly after the extinction of the dinosaurs, some birds from distantly related groups have evolved to be very similar to each other. There have been some big surprises over the years - for example, flamingos are related to grebes, bustards are related to cuckoos and falcons are related to parrots and songbirds. There have been some big projects to work out relationships so I expect the lists to be more stable in future, although there may still be a few more changes to come. Past changes (separating swifts from swallows or owls from raptors) seem normal to us now, and I think that will happen with this new list in time.
Personally I prefer that the list reflects these relationships, because I find that it makes me look at some groups in a different way. I can start to see the similarities that have remained between grebes and flamingos (for example in display behaviour) rather than the differences between them, and start to think about what the common ancestor may have been like. It makes the idea of evolution and species diversification much clearer (for me, at least).
