The situations are not remotely comparable. You can draw nothing statistical form Jones' Slam. Most members of this board could not name any other winner of the British Amateur nor could they name who the semifinalists were in the one he won. The pros were FAR batter in Jones' day than the amateurs, so even ignoring the tremendous increase in the number of great players, Jones wasn't even competing in the best of his own era in half of his majors.
Besides the Tiger slam, Tiger has had 3 years in which he won 2 majors. Let him play his other 2 majors in those years against competition that relatively speaking is not even up to the level of the Buy.com tour and then we might have some statistical resemblance between now and Jones' era. Same for the 5 times Jack won 2 majors in a year. Lest anyone think I am just plumping Tiger.
It would be like saying only 10 of the Montreal Canadiens 24 Stanley Cup championships count because there were only six teams in the league for the first 14. You can't take away their achievements just because the league has changed.