As usual I should look at the big picture first... A 20" bar will fill the need for users depending on their cutting style and wood species. I guess different dealers are ordering the 500i with what bar is best for their customers.
At first I thought they were all coming with a 28" light bar, but that seems to be not the case.
Around these parts most saws in the 70 cc class come with a 28” bar. It suits most users larger needs I suppose. When I looked at our local saw shop, they had a demo (not for sale) 500 with a 28” light bar on it. At the time, they had no idea when they would be getting any 500is in to sell. I asked if they would come with a light weight bar and what price. I was told $1300 and something and no that only included a standard bar. Light weight would be an up charge. I asked what the point was in bragging about all of this power to weight and then not selling them with the light bar? It seemed silly to me. I haven’t been back in to see if they got any saws in to sell yet.