British and American hyphenation rules differ. American hyphenation is at syllable boundaries while British hyphenation keeps etymological divisions together. And while typo-graphy might seem better than ty-pog-ra-phy, helico-pter comes across as a bit odd to most readers’ eyes.
Well, the exact locations of syllable boundaries are not always universally agreed upon. Here is one dictionary's entry for "typography" [1] which claims that US speakers break it up as ty-po-gra-phy while British speakers break it up as ty-pog-ra-phy.
In light of that, both the American rule (syllable boundary + American pronunciation) and British rule (morpheme boundary) should put a break in the same place: typo-graphy and not typog-raphy.
Oxford New American dictionary (on my Mac): ty·pog·ra·phy
Random House College dictionary (print): ty·pog·ra·phy
Merriam-Webster (online, the print edition is what the TUG hyphenation exception list uses as its definitive authority): ty· pog· ra· phy
I published a typography magazine in the late 1990s, and never once heard a single person, American or otherwise, pronounce it the way Cambridge claims Americans do.
