To answer the title question more directly, ties are very much possible at the end of a season, though rare in the case of title deciders. This year, if the 4 winners we’ve had so far proceed to win 5 races each, come second 5 times, 3rd five times and DNF the other 5, the FIA would have to break the tie however they saw fit because the standard tie-break rules do not apply. However there is only one Champion in each category, so there will never be two F1 World Driver’s Champions of 2012 – someone has to lose out, even if it is done on an arbitary basis such as what they ate for dinner after the final race (provided that the FIA takes the decision).
Tie-breaks happen nearly every year at the back of the grid and, in theory, can be left in such a way as to show 2 drivers tying for a non-title-winning position.