I've bought 2. The first had 1-3 difference. The second had 4-5 difference. As others have said, it makes no difference, if the cpu works fine, other than maybe an overclocking/cooling inconvenience
SpeedFan can be used to graph the temps of both cores over a 15 minute interval and I rarely see much difference between the two cores as temps vary from idle to full load.
Of course this is only my opinion, but I don't think a couple of degrees makes that much difference. On all of my C2D's (5x) when the chip is under a load the spread in temperature differences seems to get smaller. (I don't mean some ridiculous temperature difference, 1 - 5 degree difference is OK IMO)
Edit: Remember it seems like all temperature sensing software is not that accurate and should only be used as an indication your HSF and cooling stuff (case fans, good air flow, good seat on the HSF, good NB cooling, etc) are working properly. (even, my favorites Core Temp and TAT)