"Bling-bling" (usually shortened to "bling") is a hip hop slang term that refers to elaborate, gaudy jewelry and other accouterments, and also to a lifestyle built around excessive spending and ostentation. (Wikipedia)

Webster dictionary: flashy jewelry worn especially as an indication of wealth; broadly : expensive and ostentatious possessions

I think the key word is "ostentatious". And in laymen's terms, I would equate ostentatious to "pretentious." So...I think bling depends on the objects owner. If I'm Lance, owning a 10k bike is not bling - it's functional. If I'm a race car driver, driving a Porsche 911 is not bling. On the other hand, that gold cassette, gold crank, etc....that's certainly bling.