The real reason for the setting? Aesthetics. The 10:10 position gives the clock or watch a number of benefits:
• The hands not overlapping, so they’re fully and clearly visible and their styling can be admired.
• The arrangement of the hands is symmetrical, which people generally find more pleasant than asymmetry, making the product more appealing [...]

“A lot of people have asked me about this, so I thought I’d put the information here, linked under my home page:
 
Yes, I am the inventor of the sideways “smiley face” (sometimes called an “emoticon”) that is commonly used in E-mail, chat, and newsgroup posts.  Or at least I’m one of the inventors.
 
By the early 1980’s, the Computer Science [...]