As you might know, Apple updated iTunes, making it simpler, and removing a lot of useful features, like the "find duplicates" menu.
There is a rumor that says that they will add it back soon, but I think they removed for another reason: the duplicates are found and removed automatically.(Unfortunately just from the library, but not from the hard disk). Here are my findings.
Using dupeGuru I found about 160 duplicates, but, none of them can be found in iTunes, even if they are in the hard drive.
Look: I have two identical copies of the same song on my hdd (same artist, same bitrate, same duration, different album), but when I search it in iTunes I can't find it.
It looks like iTunes found duplicated songs and removed them from the library (without removing them from the hard drive, though).
Maybe that's why tools that scan the iTunes library file won't find duplicates, while tools that ignore the library file and scan the folder will find a lot of them. I arrived to the conclusion that iTunes will "hide" songs if it thinks that it's an exact duplicate.
More proof. I got two identical songs from iTunes Store in 2010 (The same song in two different albums) One of them is on the HDD but can't be found in iTunes
Or, again:
But, when there are too many differences, like 1 second in duration, or an "Ã " that become an "a", the entry is kept:
That's why Apple "removed" the "find duplicates" menu: it's done silently and automatically - no need to search for them. (Though, the file gets "lost" in the HDD, wasting space...)