Oh, well in that case, it's a combination of: 1) lying, and... 2) there are no better numbers available for an early stage company. You can't go by profitability or revenue early on, because there's a lot you need to do before you get your first customer, and some of that continues to pay off. So, in the absence of reliable measures of value (a long history), they make do with the least bad method available (how much did somebody guess it would be worth).

I think also, if you have to find a place to park billions or tens of billions of dollars, it's easy to convince yourself that the $10million company you're looking at is worth a billion, or the $1billion company you're looking at is worth ten billion. The alternative is to go back to your own investors and say, "sorry, there's not enough good ideas out there to invest in, here's your money back". It's got to be hard to convince yourself that's the least bad option.