What's the deal with startup CEOs making shedloads of money while his company records yearly losses?

You can make any amount your salary, but that won't magically cause money to appear out of nowhere. So yes, you would need investors if you can't pay your salary from revenue.

In theory, sure, you could start a company, convince a bunch of investors to put in a large amount of cash, and use those invested funds to pay the CEO a large salary while the company loses money. As a practical matter, however, it is pretty unlikely. If you're running a business that requires investors to put in money, it is very unlikely that those investors want large amounts of that money flowing out in salary to the CEO. It is very, very unlikely that they'd happily invest in a company paying a billionaire CEO a large cash salary.

More likely, when you hear about startup CEOs making a large amount of money, what people are talking about is the appreciation of the CEOs stock and options. If the CEO owns, say, 10% of the shares of the company and the company's value increases from $1 billion to $2 billion, someone might report that the CEO made $100 million because his stock position appreciated from being worth $100 million to $200 million. That depends, of course, on the value that others place on the company but it is vastly easier for a startup's stock price to double than for that startup to pay out $100 million in cash to the CEO.