Hi,
why recommended? Good question! ;) i remember i read it, at first, i thought on the php.net website, but now, after quite a search, they are neutral , and they don't even mention the limitation regarding duplicated named placeholders!
Another gogol search but can't find anything regarding a "recommandation".
the only point i can remember is that with named placeholders, you don't have to worry about the order you use them, while with question mark placeholders, we must take care of the proper order of the elements in the array that is passed.

Hence i suppose my brain took a shortcut and "decided" the named placeholders are "better",  (i was not aware at this time of the issue regarding duplicate named parameters, amazing they don't even mention it on the php website!)

And yesterday, the ultimate wrong shortcut was to write "(recommended)" beside 'named parameters'

Lesson: i must be more careful with my assumption... And Thanks for noting that!