anyone know?

They are different.
The chain thickness is different between 9 & 10 speed, 10 spd being thinner than 9.
The 9 speed chain rings are thicker also.
This is my experience from trying a single 9spd E13 ring up front when i first went 1x10 some time ago. The chain sucked back up around the ring when pedalled

EDIT - Didn't really read the title, ignore

nope, 10 speed runs 24,32,42 rather than the 22,32, 44 of 9speed

10 speed rings also sit slightly closer together so it will work on a 9 speed set up but not alway 100% (we've had a couple of bikes in the shope where people had fitted 10 speed cranks and the chain would climb of the middle ring as it sat too close to the outer)

9 speed is normally 22-32-44. 10 speed is normally 24-32-42 if we're talking triples.

I'm not convinced they are any different at all.

I've got a 9spd & a 10spd SLX middle chainring sat in front of me and visually they look identical. Even measuring the width of the teeth with a micrometer there was no difference.