I'm working from a list USAF published in one of their journals. There were also over 5000 helicopters shot down or otherwise lost in Vietnam vs 250 or so in Iraq and Afghanistan combined. Either the US got a lot better at this warfare thing or we are fighting people a lot less skilled at this whole warfare thing than the NVA/VC. I'd guess it's both, but I'd wager the majority is the opponents. The whole idea of projecting the future of warfare based on these wars seems kind of risky.
The NVA were, well, smart about it, though. I read loads of Vietnam War memoirs and learned how they used to set traps for helicopters. Like they would gather around a casevac and wait for the helicopter to try and land before opening up and trying to take it out. That's just one example.
At the same time those helos were susceptible to small arms fire, so you didn't even necessarily need specialized equipment to disable one or kill the pilot.
Probably there were a lot more emergency extractions done by helo back in those days compared to today. Also, I guess the enemy today just isn't nearly as smart or determined as the NVA was. I mean, today we have absolutely no equivalent to the Siege of Khe Sanh, in terms of a major military action accompanied by an international political play coming from a unified military leadership.
Even look at the Tet Offensive. The North Vietnamese government was basically willing to sacrifice the entire Viet Cong in order to shock Joe Sixpack in the US. I don't think we've seen anything with the psychological impact on the public from our current wars.
No equivalent to the Vietnamese tunnel networks either.