Idk wtf everyone is going on about it being "unneeded" for. Of course it's not needed and pointless. That's never stopped them before.
If they really wanted to, they could add in enough new features for you all to buy a copy. They do it every generation: Yellow, the original Crystal, Emerald, Platinum. You fall for it every time. And if sales for HG/SS drop before Generation 5 is ready, I have no doubt in my mind they will do it again. However, with the amount of obsessive fans that have been asking, whining and begging for these games for five years, these will probably sell better than any Pokemon game ever. So they probably wouldn't want to pull focus from them, unless everyone buys their copy of HG/SS in the first week or so, and then they need something to fill the gap between this and Generation 5.