This is true, and an interesting way of thinking about it. Too bad pro shops will not agree. They need to make their dime, and if someone comes strolling in wanting them to drill up a blank high performance ball they got for $100 off the internet, they will naturally be upset. The only way pro shops can get around this issue is charging more for drilling balls purchased outside of their shops.
Lets do the math here (Using the C System 3.5 as an example)...
& these are purely estimates, don't hold me to the numbers...
Scenario 1 (customer buys ball directly from pro shop)
-Cost of ball/grips/slug to shop: $120
-Consumer pays with drilling: $220 ($180-ball, $40-drilling)
-PROFIT FOR SHOP: $100
-COST TO CUSTOMER: $220
Scenario 2 (customer buys ball offline for $100)
-Cost of grips/slug to shop: $10
-Consumer pays for drilling: $70 (since ball was not purchased @ shop)
-PROFIT FOR SHOP: $60
-COST TO CONSUMER: $170
-Scenario 2 shows the consumer paying $50 less than in Scenario 1
-Scenario 2 shows the shop making $40 less in profit than Scenario 1
In order for the shop to make the same profit off Scenario 2, they would need to charge $110 for drilling a blank ball, which is not going to happen unless they don't want the customer to return. Mind you repeat customers will want a break on the drilling fee on top of this.
We see the customer in a win-win buying offline, and the pro shop at a lose-lose. It is unfortunate, but if the cheap internet pricing keeps up at this rate, owning a pro shop will only be a side job, which will probably be done in your basement to save rent costs.