John we're talking about two different things. "Volume" is the count of trades over a period of time. It should always be a whole number.
No it isn't. Think about how utterly worthless that would be as a metric.
You trade 1 order of 100,000 BTC = 1 volume?
I trade 100,000 orders of 1 satoshi each (0.001 BTC total) = 100,000 volume?
What use would that be as a metric?
VOLUME on any currency exchange is the amount of currency traded. MtGox measures the BTC volume (i.e. the total BTC traded in the prior 24 hours).