For PDF files outlining fonts is not necessary.
With the proper PDF job options, fonts are embedded into the PDF as live type. This allows the font to retain it's original hinting data. See here for an explanation on hinting: When is font hinting used for print?
With respect to this "girl on facebook"....
A corrupt font is as likely to happen as a corrupt file. Outlining type does nothing to prevent data transfer issues. It is just as likely that color profiles get corrupt as a type character gets corrupt. Thinking outline type prevents this is just folly.
Fonts embedded into PDF are given unique data names within the PDF. There's zero chance the user has a "font with the same name" which would alter the display of the actual PDF as it shows in Acrobat or Reader. The only time a font would be substituted for another is if the PDF were opened in some other application, such as Illustrator. However, if you send a PDF/X file for printing, the PDF/X file is used in apps such as Preps or TrapWise and rarely actually opened for editing in some other application. In addition, any printer worth their fees is going to be aware of when and how font substitutions happen. If they cause them, they better be able to fix them.
As for a PDF not containing some special character such as
å -- that's pretty unlikely as well. The font is embedded in the PDF - either the entire font, or a subset of the characters used in the PDF. If you use
å in the piece, then
å will be embedded just like if you used
S in the piece, the
S is embedded. Embedding does not just randomly decide to not include a used character.
The only reason to ever outline type is to prevent font issues when opening the file in a different work environment. However, no other application or format embeds live type. This is the difference with the PDF format -- embedded fonts. PDF is designed to be a self-contained, all inclusive, format unlike other applications. If you were to send an .eps or .ai or .psd file, then yes, you need to also send the fonts or if not sending fonts, outline the type. But none of that is needed for the PDF format, especially not for PDF/X files.
All these reasons you are citing may be valid for other file formats but not for the PDF format.