Join Date: May 2006
Location: South Shore of Montreal
The stock coolers are meant to be used with the CPU they come with and cool them properly. So, yes, they're meant to do the job fine.
The only thing to consider will be noise depending on the location of your HTPC and, in that aspect, most aftermarket heatsink are more efficient at cooling your cpu (better thermal) and/or use a fan that will be more quiet than stock cooler and/or a combination of both.
Here, my HTPC runs an AMD 3200+ using the stock cooler with the fan speed controlled via SpeedFan (software). Under 45c, it turns the fan off. Above 45c, it turns it on at ~40% (silent at ~1meter in front of the case). Above 55, 100%. The fan only turns on when I am watching HD content (temp hovering ~48c) and never at full speed. The only full time active cooling is the PSU and 1x120mm TriCool Fan running at LOW setting near the CPU as exhaust.