It's not the same if you take a closer look at the table of comparison results.
In the SystemCooling.com review, only the room ambient and load temperatures are reported using Folding@Home. It does not report thermal resistance values that incorporate both idle and load temperature and the "spread" or difference between them. However, the difference between the SI120 and XP120 of perhaps 1C favoring the XP120 in a comparison where the ambient in the SI120's test is also a degree lower does not account for this.
It may be that the idle temperature value of the SI120 is a few degrees higher than the XP120's at room ambients as low as 24C. But the thermal resistance value in the OverClockers.com review of August 27, 2005, shows a thermal resistance for the SI120 of 0.14 versus 0.167 for the XP120 using "realistic" fan speeds under load conditions.
If the operating limit of your CPU is 70C, and you have one cooler which keeps the CPU at 28C under idle conditions but peaks at 43C under load, and another cooler which keeps the CPU at 30C under idle and peaks at 43C under load -- which is the better cooler?