Give that there's too little time between the end of the championship and the beginning of the training camp and having played the all the tournaments in the past years he wants to take the summer off, to reload his batteries. So much for the official version...
...the question is, if this is the real version, why didn't he announce this before the call-up for the training camp? I'm pretty sure that there's more behind it. He's the president of the players union PSAK, in which Papadopoulos and Kakiouzis are heavily involved as well, and would've been the next one on "the list" most likely. He's aware of his small chances making the team this year therfore most likely, even moreso as he didn't play a good season.
I'm disappointed by Tsaldaris 2nd half of the season. I don't think that he's the shooter we were all looking for, not on that level. And neither Tsaldaris, nor another candidate for that spot has much experience on such a level, which won't make things easier for the team. I'd take Perperoglou, he offered some shooting solutions for PAO in the greek playoffs, and he also would be a solution for the SF position, where Greece also doesn't have much depth. Of course he's unexperienced as well though...
EDIT: Arkadios was faster than me