Just guessing here... Since veteran points functions still exist, I'd say they made that change more on the presentation level, while API remained nearly the same.
Lua Code:
-- from playerprogressbar.lua
function ZO_PlayerProgressBarCurrentFragment:RefreshBaseType()
if(self:IsShowing()) then
if(GetUnitVeteranRank("player") > 0) then
PLAYER_PROGRESS_BAR:SetBaseType(PPB_VP)
else
PLAYER_PROGRESS_BAR:SetBaseType(PPB_XP)
end
else
PLAYER_PROGRESS_BAR:ClearBaseType()
end
end
PPB_VP uses GetUnitVeteranPoints("player"), GetUnitVeteranRank("player"), GetNumVeteranPointsInRank(rank) where
PPB_XP uses GetUnitXP("player"), GetUnitLevel("player"), GetNumExperiencePointsInLevel(rank)
edit: a bit strange that they use GetUnitVeteranRank("player") > 0 to check you're veteran, in other places they still use IsUnitVeteran("player") so that function wasn't removed, either.