If the practitioners don't use AW it strikes me that either the cost to target any related term is crippling, or AW may not be as effective as it's made out to be :-)
A valid but not entirely convincing point BC
I think BuckWorks is on the right track here. Why pay for clicks when you are already at the top? I've run PPC for some really competitive terms where I ranked #1 and the PPC had SUPER high minimum bid and the traffic stunk. ROI was very low compared to the organic listing and it didn't makes sense to maintain the PPC. The logical thing to do was to allocate the money to under-performing phrases and deepen my client's saturation into their industry.
maximum ROI - SERPS
profit maximisation - SERPS + PPC
Lets use an example.
You get 10 conversion from being in position 5 in the SERPS, each bringing you $500. You get $5000 profit.
Now you start a PPC campaign. You pay $1 CPC and convert at 2%. Not unreasonable.
You receive 500 clicks from this PPC campaign bringing in 10 more sales and pay $500 for the pleasure.
You now have 20 sales waith a value of $10000 and have spent $500 to achieve this. Profit = $9500
I know which one I would rather have.
;-)
Those who had a better understanding of which links were which split where they'd click. However, those that clicked on both paid & natural results didn't choose at random, but with forethought. (I.e. - organic results when looking for info, paid results for online purchases).
If this is true, you could never maximize traffic with either/or. My guess for what the OP describes is simple economics. SEM/SEO serps have got to be high on Google's radar, and the paid traffic probably costs a fortune.
You now have 20 sales waith a value of $10000 and have spent $500 to achieve this. Profit = $9500
Remember that "profit" is not gross sales, it's what's left over after all the bills are paid. Your point would be valid as long as the business had the resources available to service those extra sales.
There may be a lot of other incremental costs and limiting factors besides advertising costs.
Depending on what your product or service is, factors like availability of trained staff, availability of credit, warehouse space, production facilities, lead time to obtain inventory, and so on might change the picture immensely.
Each business needs to plan for sustainability. Managing growth wisely is often the difference between the winners and the losers.