They accept both "want" and "need" in these types of sentences, just as they accept both for teastaigh. Which, I agree, is absolutely horrible.
It came from from your discussion of Ní raibh uaidh ach sin being translated as "That was all he needed" or something similar. In my dialect of English, however, that would still translate as "want" (He didn't want but that)
Pretty sure I was picking English to translate to Irish. Otherwise I would not have wondered about uait. I could be wrong but sometimes the same sentence is given twice in an exercise e.g., one English to Irish and then the reverse. When I have a question I go to the discussion.