As a member of the green tail brigade, I think the 250kts below 10 is a very good SOP. Esp going into some of the Greek Islands, it alows more time on preventing the ATC Controller from killing you, and a bird met at 250kts is a lot kinder to the aircraft than one met at 300+kts.
Just one thing to bare in mind is that the 250kts below 10 is not rigid, if ATC ask for a higher speed then the SOP can be ignored, as long as the captain feels that its safe.
As far as this incident, MC, either the captain felt the request was unsafe or you were stuck behind a training flight, and the captain felt that someone new to the aircraft hurtling around the sky at 280Kts at 6000ft was unsafe. I tend to agree with him.
If it makes you feel any better is happens to us also. Stuck behind a British world 737 into Faro, the GIT decended at M0.70 from FL330!! No complaints, just spent alot of time laughing at the poor b@stard