System vs. CPU temperature (7VAXP)

The system temperature on my computer is always higher than the CPU
temperature. For example, the current CPU temp is 41.1C, while the system
temp is 47C. The relative difference remains constant even under load.

From a thermodynamic standpoint, is that even possible?

I asked GB tech support if the sensor display was reversed, and they
assured me that the temperature difference would be "normal if you got a
slower CPU and better heat sink fan."

I'm running an XP 2700+ (stock timings) with a CoolerMaster HHC-001 H/F on
a 7VAXP Rev 1.2. It's inside an Antec Sonata case (380W TruePower P/S)
with a 60GB and a 200GB hard drive. All three mem slots are occupied
(Kingston PC 2700 512 MB).

I've searched for an answer to this and gotten nothing but conflicting
information. Any help would be appreciated.

While I'm on the subject, how often should the H/F be reseated and thermal
paste reapplied? Two months ago, my CPU temp was 36C idle, and now it
idles at 40-41C. I work in a relatively dusty environment, so some of it
is attributable to dust accumulation. Should I be concerned about the idle
temp? Load temp now peaks at 48C CPU and 52C system.

Thanks in advance,
Orange Barrel