In my opinion Easter Eggs are completely necessary, makes the game that much more enjoyable, allows the community to discuss the meaning of said Easter Egg and allows people to hunt for unseen Easter Eggs, adding gameplay. Please stop your trolling.
Edit: Unnecessary in the means of, if a battle takes place in space, the game makers dont ask scientists the constellation system in that quadrant in order to accurately place the stars in their cinematics and ask the entire team to make a 3d world based exactly off that environment.
Similar to how the game Prototype took place in New York City but didn't EXACTLY replicate it in order to not waste time.
When I think about it save for a meager attempt at making Central Park, the games area doesn't look anything like Manhattan.
Having a lack of Easter Eggs does not decrease the games enjoyment at all considering many players play games without knowing that the Easter Eggs even exist.
As you said, they are there so gamers can consider and discuss why they made them that way. The programmers made the games flat hoping that players would notice.
I would say it decreases games enjoyment in the long run. Lets take Assassins Creed 2 for example, lets take out all of the extra missions they put in, take out the money system, your given standard weapons the whole game, you can only play the story, etc.
I wouldn't assume a game isn't hindered by its addition of collectibles, treasure hunting, etc.
And theres a difference between adding things for fun, then adding things unnecessarily . I guess you ignored my example because as I said game makers are smart, not idiotic.
Prototype
Fast paced game that youll end up never even looking at the building your scaling
A lot of explosions, NPC's, and action
If they had made a highly realistic and detailed Manhattan sandbox area it would have overall lagged the game when attempting to play in such an environment (My ps3 lags a bit sometimes when I play the game with its low detailed buildings).
Theres a large difference between Easter Egg, and something that would be completely detrimental to the project.
Now imagine Prototype when you take a helicopter and fly as high as you can with a curved surface environment, oh joy for a few minutes that you are in the sky before you get bored you would notice the millions of lines of code to make a workable spherical surface of gameplay get bored of how unnecessary it was and the fact it just took up another few gigs (exaggerated) of your Harddrives memory and you turn off and uninstall the game for wasting your space and lagging your game because they tried to make a realistic world environment.