Yes, I realize the number of guys under 4 now but you have to consider:
1) His training was completely different. Landy at least had some base running to work with.
2) Track surfaces were slow
3) Track shoes were horrible. I have a pair of spikes from that time period. I don't even know how they put those things on. I feel like ice skates are more comfortable.
4) Lack of sleep while in med school
5) Common thought was that it was not possible to break 4.