Engines still have pushrods, so I don't think that is it. :)
Comes down to a couple reasons - 1) the increased pollution reduction technologies (i.e the catalytic converter and muffler) used, which in the video you linked to doesn't have any of those and is just straight headers and 2) the timing of those older motors is mechanical and set to be optimal when the motor is at a peak (or near peak) performance.
> the timing of those older motors is mechanical and set to be optimal when the motor is at a peak (or near peak) performance.
Not true with mechanical variable valve phasing/timing/shifting systems, famed (and defamed) as VTEC for Honda, but available in other alternative forms (and often recently and in milder forms probably due to Honda and Toyota patents gradually expiring), like Toyota: VVT-i (famous as VVT in AE86's 4A-GE engine), Suzuki: VVT (e.g on Swift Sport M16A engine), Ford: VCT...
Or it can be completely electronic thanks to direct injection gasoline engines, like Fiat MultiAir.
You're correct in saying that other factors define the sound of the engine, but note that his comparison is in this instance technically valid - the V10 in the Gallardo uses overhead cams, so there are no pushrods.
Comes down to a couple reasons - 1) the increased pollution reduction technologies (i.e the catalytic converter and muffler) used, which in the video you linked to doesn't have any of those and is just straight headers and 2) the timing of those older motors is mechanical and set to be optimal when the motor is at a peak (or near peak) performance.