i agree, don't change anything, it simply means that if you're playing a game that only utilizes one core out of the 4 that you have, that core is going to run a little hotter than the others... what do the other cores read temperature-wise?
Also, check the temperature for each core while you do not have any other programs running (save for the Core Temp)
Core = processing unit. These chips used to have only one such unit per chip. Now they have 2, 3, or 4 . . . and more are coming. Your chip, a quad, has 4 processing units, each capable of what one old PC used to do.
im not sure what the temperature of the room was when it reached 70C, but i am using the heatsink/cooler that came with the processor. i have an intel core 2 quad Q6600...ASUS. i bought it from msy technology.