From page 28 of the IWP Guide:
"Dynamic subsummary parts do not appear in Instant Web Publishing."
Is this being addressed? This one of the majors I was going to use to push the product, that it had a great web interface and we won't have to load the app on everyones computer.
I couldn't say. But you may want to delve into the IWP Guide some, and also search for pertinent threads on this forum and others. As impressive as IWP is for certain situations, it does have significant limitations.
Also, there are more sophisticated (and more difficult) options for Custom Web Publishing (as opposed to IWP). If you are willing and able to invest the time to go one of those routes, it may give you more of what you are looking for.
There are some clunky work arounds. I don't have an IWP database up yet, but sometimes you want the same thing in a portal and you have the same limitations there.
One option is to define a getSummary function in a caculation field and add one more column to your list of data.
The result would look something like this:
Fruit Qty subTotal
apple 5 10
apple 5 10
pear 1 1
plum 2 3
plum 1 3
definitely not as pretty, but it may serve in some cases.