A rebadge is a card with a changed name but identical performance. Same gpu, same memory, same clocks for both. Rearranging the pcb is nice and all, but it's still the same card. The 4870 and 4890 and the other GTX cards all have different clocks and performance. Therefore they are different cards. The GTS 250 is as much a new card over the 9800GTX+ as the Radeon 9200 is over the Radeon 9000 because it has AGP 8x support instead of just 4x.
That said, rebadging a card isn't necessarily a bad thing and in this case it makes a whole lot of sense. I don't get why people would argue in either direction about it so intently even though it doesn't matter. People still buy the 9800 cards. It makes more sense to name it GTS 250. If you compare GTX 295, 285, 280, 275, 260, you can tell which is better than the other by just the name. Throwing a 9800 into the mix can make things confusing for an unlearned customer. Changing it to GTS 250 makes everything make sense.
That said, rebadging a card isn't necessarily a bad thing and in this case it makes a whole lot of sense. I don't get why people would argue in either direction about it so intently even though it doesn't matter. People still buy the 9800 cards. It makes more sense to name it GTS 250. If you compare GTX 295, 285, 280, 275, 260, you can tell which is better than the other by just the name. Throwing a 9800 into the mix can make things confusing for an unlearned customer. Changing it to GTS 250 makes everything make sense.