Money is one possibility. I'd also wonder if maybe it has something to do with being able to A) guarantee the cell count and B) guarantee viability.
And in reality, a starter would be necessary at a much lower gravity than 1.060. Unless your gravity is 1.028 or below, and your yeast is 96% viable (basically less than a few days old, it'll spend more than that in transit to the LHBS most of the time), you're going to need some form of starter for a 5 gallon batch if you want an optimal pitch rate. That said, if I'm brewing a beer 1.035 or below, I generally don't make a starter unless the yeast is fairly old. Anything else, I do.
Souring: '14 Brett C Old Ale, '15 Lambic, '14 Lambic, '14 Flemish Red, '15 Flemish Pale, '15 Oud Bruin, '15 Session Kriek
Cellar: '10 Brett B Tripel, '11 Lambic, '13 Brett C English Barleywine, '13 Quadrupel, '13 Sour Stout, '14 Brett C Bitter, '14 Spontaneously Fermented Cider, '15 Wee Heavy, '15 100% Brett B Red, '15 100% Brett L Kriek, '15 Bière de Garde