It seems Brannon Braga has been saying quite a lot of stuff lately. I just saw a recent youtube video where he said the original idea for Enterprise was a multi-season long story-arc with season 1 primarily be an Earth-bound series. It starts almost identically as we've seen in Broken Bow, but most of the season 1 was going to be about the rush to get the NX-01 built in order to handle Suliban threat and season 1 was going to end with the launching of Enterprise. Apparently, TPTB insisted on using the old TOS/TNG/VOY episodic "starship encounters alien of the week" formula so Braga was forced to launch the Enterprise in Broken Bow.
That sounds mostly in line with what Braga has said over the years. The original idea for Season One (or at least part of it) was to have it set primarily on Earth, with Archer putting his crew together while the NX-01 is under construction.