In the case of Teddy Long, his WWE contract expired. He had been taken off TV for some time and it was well known in the company that he was going to be departing the company.
In the case of Yoshi Tatsu, there was a feeling for some time that he had really regressed in the ring. The company had attempted to find another role for him, including trying him out as a ring announcer in NXT.
Regarding Brodus Clay, the feeling among those I've spoken with is that he fell out of favor with creative, which was obvious when they broke up his team with Tensai and then did nothing with him. His final appearance for the company was putting over NXT champ Adrian Neville on TV, which was a sign there wasn't a plan for him going forward.
We haven't heard much in the way of Evan Bourne's release but he hasn't wrestled in a long time on the main roster after being hurt in a motorcycle accident while waiting to return to action following a Wellness suspension. There was always a ton of potential for him in the ring but the timing was never in his favor.
The departures of Curt Hawkins and Camacho were the biggest surprises amongst people in the company we've heard from. Camacho was extremely popular within NXT circles and had a strong charisma and was well spoken in recent appearances. Hawkins had several more years on his current deal and had been considered a good hand in the ring, although he had not been utilized beyond putting people over in recent months.
Hawkins has a school he opened in Long Island, so he was already preparing a "Plan B" for himself and will likely get a ton of indy work in the Northeast.
The belief is there may me a few more releases among the wrestlers, but when releases happen, paranoia does kick in and everyone begins to freak out, so we will see.