http://forums.battle.net/thread.html?forumId=12014&sid=3000&topicId=27800609919&pageNo=1&

Update.

For some affixes the affix levelreq may be calculated as 75% of the (affix) level, including in this case, but it's an important distinction that affix levelreq is by definition and not following a formula.
This 75% rule can be traced back to the old classic days when it was valid in general, IIRC.

Nowadays it's just a rule of thumb, broken by many affixes.

Send an email to MartyT and he can get your chars done rather quickly.
He's already taken care of all of mine.

I have a challenge for you. Show me 2 diadems with 1 socket and level 67 requirement. The chances of a rare diadem dropping are just so small, that most of the legit ones that exist are upgraded from circlet/tiara with lvl 72/79 requirements. The ones that are imported are always given two sockets.

It's quite astounding how many people forget the basics of this game, and A1 quests by the looks of it.

Diadem is the No1 thing to imbue, because you can keep rolling it forever with Pskulls. You can also imbue one with a level 8 character since all affixes are always available.

The last thing in the world I would do to obtain a diadem would be to upgrade which is a complete waste of good runes and increases the rlvls.