Its what MJ said, a heavy flywheel, coupled together with an ECU design. If you shut the throttle too quickly on catalysed cars, you destabilize the flow and possibly the mixture of exhaust gases through the cat, decreasing its life.
Modern cars hold the ICV open slightly when you shut the throttle to prevent the engine revs dying back too quickly, and to keep engine mixtures more consistent, to try and preserve the cat.
new wheels
Added to the fact the 1.7 that MJ is used to driving (in the loosest possible sense 
) has the smallest flywheel in the world! Revs really are very fast changing compared to the other 2 engines.
) has the smallest flywheel in the world! Revs really are very fast changing compared to the other 2 engines.'89(G) 340 GLE B172k
'03 S60 D5 SE, '91 (J) MX5, 1954 Cyclemaster
Ex:
'89(F) 340 GL F7R (ex B172k) - Fake -> SBKV 300 Runner Up 08, 12; '91(H) 340 GL B14.4E - Kar; '88(F) 360 GLT B200E - Jet -> BKV 300 Runner Up 09; '89(G) 360 GLT B200E - Beast
'03 S60 D5 SE, '91 (J) MX5, 1954 Cyclemaster
Ex:
'89(F) 340 GL F7R (ex B172k) - Fake -> SBKV 300 Runner Up 08, 12; '91(H) 340 GL B14.4E - Kar; '88(F) 360 GLT B200E - Jet -> BKV 300 Runner Up 09; '89(G) 360 GLT B200E - Beast
