Santorum was all puffed up because he claimed three victories in three states totaling fewer voters than Tulsa has by itself.
So yeah, he can win the primary and lose the Presidential contest. Give or take a third of the American vote is Republican. For either a Democrat or a Republican to win, he needs all of the votes of his own party and either half of the independents or some combination of independents and crossover votes. Santorum can't do that.