You are hand-waving away this step:

"...once you have enough vendors accepting Bitcoin..."

There is also some irony in this statement:

"people are still clinging to bitcoins like gold"

Lots of people have gold but you would be hard-pressed to find any shop that accepts payments in gold.

I'm not really intending to hand-wave it away. I just assumed it would come to pass, based on past evidence (there's more vendors every day, with the pace accelerating). I may be making an incorrect assumption. There are, in fact, a lot of assumptions being made by those who are bullish on Bitcoin, and some or all of them may be wrong. In some cases, if the assumptions are wrong, it will mean the end of Bitcoin. In others, if the assumptions are wrong, it'll just mean Bitcoin is more limited as a currency than we might like.

But, it can't be anything other than a hypothesis until it is tested; neither you, or I, can know how this is gonna play out. Bitcoin isn't quite like anything else that has existed before, including gold or other currencies, so we're all guessing. I've laid out what I think will happen, and a bit about why I think it will happen.

One last point: Gold, precisely unlike Bitcoin, is not easily or cheaply transferable over the Internet. That's a big distinction and, I think, enough to make it clear we're dealing with a different thing entirely. I left it unstated before as I kinda felt it would be obvious to HN readers. But, any time anyone compares Bitcoin to gold or another traditional currency or store of value in a general way (without being specific about how Bitcoin seems to be behaving like that other subject in one way or another), I question the validity of the analogy straight away. I genuinely believe Bitcoin is something new, and new human behaviors will develop around it.