hmm, basically downloading is the same.

When downloading segmented the chunck/partials might be much bigger, up to the full file size. Swarmed chunks/partials are small, a few 100KBs or whatever will fit best to the needs of making modem users part of the network.
Segmented downloading and swarming does NOT exclude each other! Swarming is just a "bonus". One advantage of swarming is that e.g. resuming should be improved, because the files have been distributed all over the network and therfor offer more alternative sources.