1. It is held once in four years, making the chances to get the title less in a player's career.
But only 8 players can make it to WTF. If you are a regular in the top 30, you have one or two chances to go to the Olympics. It's not that difficult for a player to make it, unless you're from France or Spain and have to compete with other guys. WTF is much harder to qualify for and the chances to get in are way tougher.
Yes, Olympics is the 5th major and anyone who disagrees needs to get their head checked.
While we are at it, let's not forget that Miami, Indian Wells and Abu Dhabi are also the 5th major. So, we have 4 "main" majors, and 4 5th majors.
Cincy is the true 5th slam.