Yup. The R520 and R580 cores run pretty hot. They have about 300+ million transistors (mainly becaus of the Ring Bus Memory Controller), which is why.
The X1900 stock cooler is actually not bad...it's like a giant hunk of copper. The only thing that sucks about it is that it's heavy as hell and to cool efficiently, it needs to be at maximum RPM, which is LOUD.