You've gone too far here and got yourself in a bit of a mess again.
Giving general injury updates is indeed common practice. It helps inform fans, gives Pellegrini something to say in press conferences, and journalists something to write.
I'm guessing by the tone of your posts that you don't live in the UK, so you might be unaware how big a role the UK press plays in setting the public agenda of discussion, particularly on Sport. Ferguson was the absolute master of controlling the media and using it to his advantage. Putting pressure on opponents, opponents managers, opponents fans, referees, referee selectors, FA officials, deflecting unwanted attention from his own players, and giving certain players a confidence boost or encouragement.
Because he was so successful, and I hate to say it, so engaging and charasmatic in press conferences, journalists and newspaper editors hung on his every word. Anything he said was newsworthy. Ferguson would actually dictate the footballing agenda in the media by what he said in press conferences. That yielded huge influence. What he said got blanket coverage in the press, and in turn caused huge debate on TV, social media, in the pub, wherever. It would be naive beyond belief to think it didn't also trigger discussion among opposition managers and players.
As
@tolmie's hairdoo @SWP's back and
@Zin 'messiah' Zimmer have pointed out to you, Fergurson would regularly use it his advantage when the press asked him who was available. For example if Berbatov was injured for 6 weeks and back in Bulgaria, Ferguson would say he was training well and would probably start on Saturday. The opposing manager might then spend the week preparing to play a high line because Berbatov had no pace. Come the weekend, he'd play Wellbeck who had pace to burn, totally dumfounding the opposition manager, and giving his team a strategic advantage in the game.
The best example I can think of is one derby when Yaya went away for the Ivory Coast training in Paris prior to the ACN. Fergurson came out and said to the press that City were playing games with the media and he expected Yaya to play. All of the talk in the press and around football in England that week was whether Yaya would play or not. An hour before kick off the Shite's team was announced and Paul Scholes was in it. He'd retired 6 months previously. They had managed to register him again as a player without any of the press realising. Fergurson had completely deflected attention away, and all of City's preparation in the week was torn to shreds. Facing Paul Scholes was a very different prospect than facing Anderson, or Cleverley or whoever.
The issue with Pellegrini this week is no one expected Kompany and Silva to back. Everyone expected Sagna and Delph to be fit. So the team everyone thought we would start with included Delph as a left midfielder, where he's been pretty poor. With the players we have available, everyone seems to be in agreement we're going to switch from a 4231 to a 433. If Spurs thought we were going to start with a 4231, they would have prepared to flood central midfield, pressure us and outnumber us in there, like so many teams have done before. If they'd come out set up that way, and we had 3 centre mids like we are going to, it completely negates their game plan. It's advantage City, we've got the upper hand.
By releasing the information 48 hours before the game, as Tolm said, it gives Spurs bags of time to change their game plan and prepare accordingly. Advantage Spurs.
I understand where you are coming from that tactically it might not make too much difference Spurs knowing Kompany is playing 48 hours in advance, but psychologically it makes a monumental difference. If Kane went to bed on Saturday night thinking he's coming up against DeMichelis on Sunday, someone he can probably outmuscle physically and beat for pace, he's going to be confident thinking he's in for a pretty easy game. If an hour before kick off he hears Kompany is back, it would be a massive shock for him. He can't outmuscle him, can't out pace him, so it's going to have to play a very different game. The week he has spent preparing to face DeMichelis is now out of the window and he's facing the best centre half in the league. Advantage City.
It's similar to the Scholes story above. Tactically, it might not make a huge difference swapping Kompany for DeMichelis. But phychologically, it is a huge difference for the opposition facing Scholes instead of Anderson, or Kompany instead of DeMichelis.