According to this link, Sheikh Yusuf Al-Qaradawi has said that men cannot wear necklaces of any kind:

http://infad.usim.edu.my/modules.php?op=modload&name=News&file=article&s...

Accourding to this link, Sheikh M. S. Al-Munajjid says that men cannot wear any necklaces, even if they are made of silver:

http://www.islamonline.net/servlet/Satellite?pagename=IslamOnline-Englis...

According to this link, it is Haram to wear a necklace even if it is inscribed with a passage from the Koran:

http://www.islamweb.net/ver2/Fatwa/ShowFatwa.php?Option=FatwaId&lang=E&I...

I'd be inclined to think that there are religious overtones to this issue.