Are there any officially stated reasons why the bard was removed from 4.0 main class roster ?
It wasn't, it just wasn't in the first players handbook. Player's Handbook 2 defines classes for Avenger, Barbarian, Bard, Druid, Invoker, Shaman, Sorcerer & Warden.
My first, and so far only, D&D4 character is a bard. It works as a "Leader" type role, balanced between healing/buffs and some shiny damage effects.
I'd guess that they got stripped from the first 8 classes in PHB1 so that could have two examples of each of the new "Roles" attribute (Leader/Striker/Defenders/Controllers)
It's in PH2. As a marketing approach, they have to reserve classes (races/monsters/etc) that have a following for later books to drive sales. Also, see this wiki article for a history of the D&D bard.
This is not an official answer, but they could only include so many classes due to space constraints. They wanted to include a lot of the old favorite classes, but also wanted to include a few of the new classes to show what 4E as a system is capable of doing. Something had to be cut from the first Player's Handbook. They chose the Bard class along with others.
The only reason this is an issue at all is because everyone has their favorite class and they feel slighted if it their favorite that is cut; in this case the Bard.
Also it is my understanding that the Bard class was not completed by the time 4E was released. There were a few thematic issues they had to resolve for the class and they decided to devote their time elsewhere.
As a side note the Bard was not an initial class when D&D 1st edition first appeared as a game. It came out later, so the precedent for the Bard class not appearing in the first book had already been set. Some Old-timers do not see the Bard as a core class.
Well, there's a limited amount of space, and I think the bard just wasn't ready to go by the time the first PHB was ready, but it was one of the first classes to end up in DDI, long before the PHB 2 came out. I definitely consider it to be part of the main class roster.
The reason the Bard was removed from PHB1 was the emphasis on 4e of giving every class a distinct role, and making sure everyone had something interesting to do each round. Several classes, particularly as they were handled in earlier editions didn't fit in to this paradigm (although the Bard could have arguably been a leader instead of the Warlord, but the Warlord was one aspect of the Bard highlighted). There was likely also some "market research" going on, showing the Bard wasn't popular (The Gamers: Dorkness Rising is anvilicious about that), so it may have been taken out because most players wouldn't have gone for it (again, according to their market research, although Mike Mearls mentioned that there may have been a problem with that logic, in his example he talked about Gnomes though).