Subject: Re: YouTube “King of all media”
could be worth anywhere between $475B and $550B,

Could be more.

I heard one estimate of Youtube's profit margin of 38%.
If the revenue run rate is your $54.2bn figure, that suggests a gross profit around $20.6bn.
If that is gross (I don't remember where the 38% came from), let's knock off 21% to pencil in net of $16.3bn.
Apply the multiple given to Netflix, 47 last I checked, and that gets you to Mr Market thinking they'd be worth $765bn.

(no, I don't believe this is the right number, but it's a line of reasoning that a stock broker might use)

If one were to buy that sort of valuation, it means all the rest of the earnings, from search and cloud, are very cheap right now.

Jim