You're not understanding what I've written (or tried to write).

Why would one not want to have the anchors simply because there is no term that exactly starts with those two letters?

Your example just now assumes that words with different starting letters are on the same page, which is not at all the scenario proposed by the OP. I'll summarize again what's being discussed.

1. hacker wants to have a page per letter of the alphabet.
2. Entries on each page will be arranged alphabetically.
3. Each page will be separated into sections based on the second letter of the entry.
4. The choice was made to have these sections start at the vowels.

Given the value of the same breaking points for the sections across pages regardless of the actual distribution of entries and the need to use extra memory to do otherwise, I see no reason not to have the labels present whether or not the data provides an exact substr(0,2) match to the label.