The part about using iStock was more for temporary landing pages, say, to test out interest for a product.
I didn't know it was explicitly forbidden by their terms of service, although I wonder where they draw the line between a "logo" and an "illustration".
To me it seems like their restriction applies to using stock art as an actual logo for a real product, not as a quick placeholder for an MVP or landing page.
I enyoyed reading your article and bookmarked some links. But even using iStock for landing pages can get you in murky waters. Just ask twitter (they used a birdy from istock. After they became successful this was easily copied by copycats with almost the same url. The birdy can still be used today as it's royaltyfree). If you're going for stockart at least use it as a base for your design, not as the design.
I didn't know it was explicitly forbidden by their terms of service, although I wonder where they draw the line between a "logo" and an "illustration".
To me it seems like their restriction applies to using stock art as an actual logo for a real product, not as a quick placeholder for an MVP or landing page.