Why would they make the same mistake in this game as with Fallout 3? The game just ends and you cant continue. Are they just doing this because they know they can make a money from a DLC like Broken Steel?

The game just ends because the majority of sidequests have an impact on the ending. Theoretically, you should have done all the ones you wanted before you did the final quest, just like the huge message box warning you that the game is about to end tells you.

But perhaps you can answer the question: What is the difference between playing after the ending and simply taking the huge message box's advice and exploring to your little heart's content without doing the final quest?

http://www.gamesas.com/index.php?/topic/1131103-the-game-has-ended-oh-no-what-am-i-supposed-to-do/

You can pretty much expect me to post it anytime one of these comes along.

This has been known since at least the middle of this year. From the interviews, it seems that Obsidian just didn't feel like making post-endgame content, not a money-grab.

They're doing this because that's the best way to end the game without hitting the limits of the game disc "storage" and it explains how your actions have changed the wasteland. This isn't a big deal, it's impossible to script an open ending due to all the changes you can make, and they will not have you buy a DLC to keep going in the game. The only problem I saw with this game, is that the storyline ended abruptly. "Hey, thanks for saving our most precious leader, now go save us all from these guys. Okay, thanks for saving us from those guys... You're still not one of us." Your only options are to end the game with the dialogue. T_T

Hmmm a game with an ending. What a novel idea.

Like others have said, you get a BIG GIANT BOX warning you before you go on with the final quest. If you don't want to finish it just yet, then explore. Complete side quests. Go hook up with a prosttute in Vegas...