If one bothers to care about heat sinking, they might actually test the thing and opted not overdrive it. It's just a good totally layman indicator.
Funny enough most mains/350V DC, chips tend to have a limiting resistor for the current drive - lower resistance = high current. Most (if not all) have two resistors in parallel (for a better control, and less power per resistor) - desoldering one would greatly improve the lifespan for a minimal luminosity loss. So by picking a larger heatsink, they might picked a bit large value for the resistors as well.
