Bitcoin will soon be forced to become centralized for it will fail.
The reason: Transaction Volume
Bitcoin and other altocoins face a serious transaction volume limit problem, and will force it to become centralized in the near future... See the following videos below:
Gavin Andresen talks about it: http://www.youtube.com/watch?v=EIIkHfU2o8Y
This video breaks it down: http://www.youtube.com/watch?v=ZEgj_whkg08
How is PPCoin any different in this sense?
Because Peercoin's transaction fees are fixed and they scale with price. See below:
If the price of Peercoin goes to the level Bitcoin is at today, it will cost over $1.00 to do a transaction. This will reduce the volume. It is the price you pay to keep your money "decentralized" and it is very worth it IMO.
Other altcoins have similar issues, but I believe the fixed rate transaction fee that has been built into PPCoin will stand the test of time, and work quasi-automatically to prevent against the need for centralization.