There is no need to make a starter with a dry yeast packet. The dry yeast has plenty of viable yeast cells to just go ahead and pitch it. There really isn't even a particular advantage to the rehydration unless you are using the dry yeast on a high OG beer, which most people wouldn't anyway. You can just pitch dry yeast directly into the wort and oxygenate/stir the crap out of it.
As far as the other question, you may be mistaking the visable signs of fermentation for the actual fermentation. The batch with the higher gravity is showing more visable signs of active fermentation than the one with lower gravity, which would be expected because there is more sugar for the yeast to eat. However, that doesn't mean the lower gravity wort isn't fermenting just as fast. I've had beers ferment out completely with little to no visable signs of fermentation, including a hardly-distinguishable krausen. Less available sugar also = less visable krausen.
Everything seems normal!
Question...if all the wort came from the same brewday batch, how did the "main brew" have a higher gravity than the "extra" wort? Why wouldn't they be the same?