as for syncing, i am guessing, xbox is one system so it didn't need to sync. sony has ps3, ps4 and vita and they all show and register trophies at that same time so it needs to sync somehow.
i wonder if 360 and xbone works this way now?
that's not what syncing means in this case, i only have a ps3 & you always have to manually sync just to get any changes to appear on the sony site, otherwise all trophies are strored locally on the console
it takes a while since i bet it's manually going through each game, so the more trophies/games you have, the longer it takes (i can confirm it taking longer as i got more trophies & started more games with 0 or 1 trophy out of 20+ each)
to speed this up on ps4, they probably have a timestamp system that would skip already synced trophies, probably like SVN/GIT/dropbox version control