You guys ought not compare the delay of this game to twilight princess. Both were/are delayed for diffrent reasons.
First off, twilight princess, like many of miyamotos games, had at least one point in development where they pretty much completly started over from scratch. This can make the dev time ridiculously longer. Secondly, the reason why it was delayed from late 2005 or whatever to 2006 was because of company politics, as they wanted to have it be a wii game. Of course, the wii wasnt coming out until late 2006, and they didnt want to release the nearly complete gc game until the wii one was ready too. The period between, oh, march 06 and it coming out was pretty much them converting it into a wii game, while very little actual development was being done, indeed, it was probably pretty much done months before it was out.
Finally, many of the games flaws arnt as easily fixed by simply "adding extra dev time". The games design was pretty much decided upon from the start, and theres no signs of any areas being "incomplete" or anything. From the looks of it, the game was exactly as they wanted it. As said, the reason fro the delay was because they wanted it on the wii.
Brawl is diffrent. It isnt story based and structered, its based heavily around content, most of which can be added arbitrarly, and extra development time means they are adding more stuff. Extra characters, stages, events, subspace levels, animations, trophies and modes. It also means more balance testing. And if you really want an example why they want to put more time into it, look at melee, which had about one 3rd of its cast being clones, and modes like adventure, allstar and event were lacking depth.