Shatner has said repeatedly that he barely KNOWS Takei.
Yeah they worked together 50 years ago, and on the movies, but face it, Sulu was a minor character.
Shatner was only close to Nimoy, the other actual STAR on Star Trek.
He's mentioned being friendly with DeForest Kelley, but pretty much as a "work" friend.
The others he barely interacted with outside of the show.
He even forgot Chekov's real name, when introducing the cast at some ST event.
To this day, he still pronounces Takei as "Ta-kye", which George just can't get over.
I think they settled around Kirk, Spock, and McCoy as the three stars, with occasional bits for Scottie and Uhura. Chekov and Sulu were good for an “aye-aye” from time-to-time in response to an “all ahead full” at the end of the show. The fact that Shatner hardly knew a bit-player like Takei isn’t really all that surprising. What is surprising is the tremendous mileage that George managed to get out of a show that lasted 79 episodes in which he was a very minor player.