I don't see why everyone complains about Hamilton "cruising for 5th" at Brazil. The only reason he could do that was because
during the season, he scored more points, and therefore needed 5th
or better. Hamilton didn't "take it easy", he certainly didn't want to get overtaken by Vettel, and certainly didn't want the rain to send him down the order. In a dull-as-dishwasher dry race, he would've finished 3rd or even 2nd - but Massa truly was unbeatable at Interlagos.
Here's a thinker, Islamatron: Imagine the final race, Hamilton has 5 wins, 5 seconds, 6 thirds, and Massa 4 wins, 5 seconds, 5 thirds. Would he even bother starting his car? There would be no mathematical possibility for Massa to win the championship, and Hamilton could just as well start dueling with the Force Indias for fun. In
every system where achievements are combined over the course of the season, one driver will have an advantage and won't have to push that hard. The only way around is a NASCAR-esque "Chase" system that counts only the final race(s).
As Ciro wrote, only 4 races were won teams outside the top 4 (and, since the mid-'80s, these four teams in various guises have won the majority of races) - but even then, depending on season and race, it's usually one team that has the upper hand. McLaren didn't stand a chance of beating Ferrari at Barcelona, and Ferrari didn't stand much of a chance of beating Hamilton at Shanghai. During those races, the other team could push until they're blue in the face without getting more than 3rd or 2nd.