I would bet my mortgage that the dimensions and materials of the crank, con rods, bearings etc. of the original 136 bhp 10 valve JTD are exactly the same as they are in the latest Brera, 159 etc. 2.4's. In other words, a remap/chip is just achieving what the manufacturer had it lined up for at the next model engine development anyway ie. eventually 225 bhp in the case of the Alfa 2.4.
And just because you have more bhp does not mean you drive any faster from A to B (except when overtaking more easily and safely than before ), so 95 % of the time the load on the gearbox, clutch and engine is exactly the same as it was before the remap/chip.