Gold is different because there are a lot of good reasons to buy gold. Not gonna bother listing them.
Compelling argument. 
However gold isn't valuable because of it's intrinsic value, which is less than steel, but because of it's scarcity which gives it an actual value that is very high.
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Just because merchants are accepting bitcoin doesn't mean people are going out and buying bitcoins to spend at said merchants.
With Silk Road people have.As for the other services, what they want isn't necessarily listed.
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And guess what those merchants are doing a soon as they receive bitcoins as payment for goods and services?
Convert it into Bitcoin, obviously because the market is new, and not very large.As the market expands people will convert their BTC to USD less often, and a large portion of bitcoins can be spent on whatever it is they need.
There will be a lot of conversion at first, and then people will find the things they need still in the Bitcoin market, it's simple.