No, that’s not the problem. The Clip has a very limited power supply, due to physical constraints. Despite this, we have a long operational life on a full charge. This is possible by carefully managing the device’s power consumption.
Decoding at various clock speeds is possible by modifying the PLL parameters and clock dividers. This was done previously, as discussed. Please take into consideration that the Clip and Fuze each have several different variants, the revision 1 and 2 families. Each of these has a different configuration internally.
The Fuze has different display and memory requirements (TFT display and µSDHC socket), plus video. The Clip has two revisions, plus the new Clip+ has integrated µSDHC capability. The original Clips have the illuminated control buttons.
In short, it’s not just a matter of tinkering with the PLL algorithm, there are issues unique to each revision and device. Note that the Clip+ is closer in measured speed. Slotmonsta is right, there are many issues behind the scenes that affect the final firmware releases. A far greater number of users would be upset if the battery life dropped considerably, I would bet. A happy balance between processor demands and battery life is the “holy grail”.
Time permitting, future firmware revisions will get us closer to this goal. And there are cool things “behind the scenes” too, that require time and effort.