"And how would falling commodity and durables prices cause inflation?"
As consumer goods become less expensive (either realistically or perceptionally) it can lead to increased demand. Increased demand for goods can have a marked effect on inflation, normally it's a short term effect, but it can be enough to cause a bump in interest rates to make sure that it's a controlled effect.
Where I would expect concerns to rise about inflation is if gasoline prices really start to tank. With less worries about short term gasoline prices, people will be more willing to consider spending on other things. I know when gas prices started to jump I really cut back on my other spending. Then I got a job 2 miles from the house and now a tank of gas lasts a month.
As for copper prices, tanking badly is, I think, something of a relative term when you consider that they're still well above what they were when the latest rise cycle started in 2003. That's more of a reaction to the slowdown in the new housing market in the US than anything.
"China is not going to stagnate... their economy is growing at 10%."
Nothing is forever. I remember when people said the same thing about Japan. Now Japan is in its second decade of growth stagnation.
An economy that's super heating can be a dangerous thing.
