Is an extra 1 W that significant with LED bulbs?
There are two completely different thermal objectives
First, don't set other stuff on fire.  That's decided by the thermal insulation of the fixture (think: thick insulation in down lights) and limits the size (in actual wattage) of any bulb, but it's mainly aimed at incandescents.  Incandescent bulbs love hot places and work better there.
A fixture succeeds at this goal if it has plenty of insulation and creates a little &quot;oven&quot; for the incandescent to burn in.
Second, let the LED keep cool.  The LED cannot tolerate high temperature - neither at the LED proper or the electronic driver.  Its worst worst enemy is itself: even with their good efficiency, still nearly 85% of its actual wattage is turning into heat at the LED or driver.  The  heat will cause premature failure of the LED.
A fixture succeeds at this goal if it provides an easy way for heat to be convected away from the bulb location.
These objectives are at best unrelated, and at worst conflicting. For instance a well-insulated, embedded-in-ceiling downlight might protect from incandescents but cook LEDs.  An antiquey lamp with &quot;lamp chimneys&quot; might work great to convection-cool LEDs, but with incandescents, scorch the ceiling above it.
The fixture's LED limit applies to the second thermal objective.  It is saying &quot;Above 9 watts, we can't guarantee we can keep that LED cool enough for it to have a long life&quot;.