Swordscythe is right. I've seen some over-eager hype machines go into action far too soon and public interest peaked before the product was out - after which, the only way is down. That kind of thing actually loses sales.
I think Larian have kept the balance about right in slowly rising the profile of their game as launch nears.
Turi - the problem with the 'rely on online marketing' model is that the only people who will find out about the game that way are hardcore gamers with a definite interest. By far the largest number of people who buy games are more casual and buy stuff that looks cool or that has good word of mouth.
Online marketing does have a cost too, BTW, as you need people to do it and people cost money for salaries. Not to mention the various normal expenses of running an office. It's cheaper than many other methods, yes, but it's not free.