Tournament after tournament, it's as if pundits have no memory of previous World Cups. Today, we heard "who would have thought that Slovenia would be top of the group after one game". The answer: anyone who remembers England's habitual sluggish performance in the first group game; and anyone who knows that Slovenia only conceded four goals en route to the finals.
There is a remarkable degree of predictability from tournament to tournament. For instance, there hasn't been a new winner of the tournament that wasn't the host since 1958 (this should give pause to those falling into the trap of tipping Spain on the basis that they look like the best team). No European team has ever won outside Europe. There are usually a majority of European teams at the quarter final stage - expect five or six to make it through this time - even though the final is usually a European team versus a South American team.
But there are margins of unpredictability (even if these are, to some extent, predictable). In the group games, established teams being beaten by less fancied sides has been familiar for a long time: think Scotland's demolition of Holland, Algeria beating West Germany, Cameroon shocking Argentina, the USA upending Portugal. Note, though, that these defeats didn't tend to harm the 'bigger' teams in the long run: despite being victims of these shocks, Holland, Argentina and West Germany still made the final; only Portugal failed to make it out of the group*. You can guarantee that one or two major teams will not make it to the quarter finals, and that some lesser known teams will make it that far. But none of the 'smaller' sides has yet made it past the semi-final stage (Turkey reaching the semi-final in 2002 was the furthest that one of the less successful teams has gone in recent tournaments). The last time that the final was contested by a team that wasn't a previous winner or the hosts was 1978, when Holland lost to Argentina.
*Thanks to Graham Harman for correcting an error I originally made here.
And I forgot the Republic of Ireland's defeat of Italy in a group game in 1994; Italy fitted the pattern precisely, by eventually reaching the final. (The fact I forgot this match underscores Giovanni's point below that the 1994 tournament did not happen. It's the one tournament since 1978 of which I have almost no memory.)