He’s dyslexic.
He’s joking about it.
and 2. are unconnected. It would be a joke whether Leno was dyslexic or not; the only difference is that his actual dyslexia allows him to say the joke without the PC police complaining that he’s making fun of misfortunes*.
*The definition of humor, BTW.
Why would you say this? He is dyslexic and is well known to be one. This does not mean that he has not overcome it by learning how to read properly anyway.
Tom Cruise is as well, I think, yet he manages to read and memorize his lines.
Xenu must help him with that.
But yeah, I’ve heard Leno mention his dyslexia (usually after flubbing reading something) but not really as a joke, just as an explanation why he flubbed.
Heh. I’m not dyslexic, but that’s my goal, too! 
The editor here drives me nuts sometimes, with those little red underlines of misspelled words. Often, I’ll tweak and tweak and tweak, and never get that damn thing to go away. I’ve contemplated punching my screen and yelling: Just fucking tell me how to spell the damn word, why don’t you!! I guess I could just use Word and cut and paste, but too much effort…
Right-click the underlined word.
My brother was dyslexic. I bought him a tee shirt that said
DYSLEXICS OF THE WORLD…UNTIE
A friend had a bumpersticker of that in her locker, I was the 1st one to get it!
Goldie Hawn is dyslexic; it was a plot point in at least two of her movies, Protocol and Overboard.
Obligatory xkcd.
My youngest son has Dyslexia (and Dysgraphia) with an actual medical diagnosis (you would be amazed how many claim the disorder without this). He has the added joy of being “Gifted but Learning disabled.” Great fun trying to get the schools to help with a student who is not disruptive and an above average student.
Anyway, if you read him a paragraph he can recite it back to you word for word. If you ask him to read it and recite it… probably won’t happen. He has spent several years going through the Ortin Gillingham program which we were very fortunate to get from the local Mason’s (otherwise many, many thousands per year… I have a deep respect for the Mason’s) which has helped immensely.
Most people don’t get the disorder… and yes I have a sense of humor and have no problem with the “Untie/Unite” jokes. Unfortunately it isn’t as simple as mixing up letters.
As far as Jay Leno goes… what he does is fully within the capabilities of a dyslexic person.
The spouse is a clinically-diagnosed high-functioning dyslexic and has managed to get a PhD (complete with 600+ page dissertation). She can read just fine but can’t spell worth a damn and frequently leaves out entire words when writing.
That said, Jay Leno is still a dirty liar. He said that he loved me and that we would run away to Tahiti together! That bastard!
Yeah, and he called me a nerd in front of a room with about 200 people… oh wait.