This is a very cultural westernised ideal, where girls grow up envisioning what her diamond will look like, with the encouragement of her mother. The BBC actually did an excellent article around the price of an engagement ring but it also said the following:
'Prior to the 1930s, presenting a woman with a diamond engagement ring was not the norm. Even on the eve of World War Two, a mere 10% of engagement rings contained diamonds. By the end of the 20th Century, 80% did.'
When I visited Eastern Europe recently, it was obvious women didnt wear diamonds and most people were unable to tell you what they are or look like. They wore gems that you would relate to a birthday stone.
I think the celebrity culture has a lot of influence over girls and what they think is trendy and its very rare to find a celebrity who isnt showing off their latest diamond bling.
The BBC article can be found at - http://www.bbc.co.uk/news/magazine-27371208
The implication that girls as a whole tend to love anything a lot implies the generalization that all girls are similar, which simply isn't true. By saying that girls tend to love diamonds, a stereotypically female trait, you are boxing them in to the female gender role. The female gender role also includes the idea that women are subservient to men, as has occurred in history.
I know you're not trying to be sexist, but unfortunately that is the implication of the topic, as often happens in modern times.