The only differences were birthsign and race, and these were a limited choice, many birthsign powers being massively overshadowed by doomstones, and many racial abilities becoming obsolete, summon a ghost once a day at level 30?
With 50 perks out of 280, your end game character will be unique, even with all skills at 100. One obvious benefit to this is replay value, playing a thief or mage requires serious investment in perks, with other areas suffering, so you can play a new character totally different the second time.
Is it actually confirmed anywhere that some perks have skill requirements?