Hi Vilas,
72kts logic for ground spoiler activation during RTO is common. (same as B747-400 from memory)
The 40kt logic is to prevent a dozy crew hurting standing cabin crew if they select MAX autobrake during taxi out and the ground spoilers haven't been stowed from the previous landing. I know it's hard to believe but some manage to miss it during the after landing checks and pre-departure checks. I think it will only activate the MED setting below 40kt. (I've never tried it myself).
That's why the flight control checks are performed before the MAX autobrakes are armed during taxi out. Hopefully the dozy crew will then notice the ground spoilers are still deployed from the previous landing.
Last edited by Goldenrivett; 26th Jul 2016 at 15:15.