True, Iron Man, Cap, and Thor showed up for the induction, but they were basically just guest stars in the Avengers at that time. Not really "on leave" as much as "on loan". Usually, they'd rotate them around a bit, Cap in one adventure and a few issues later Iron Man would pop in. There's always been this weird territoriality with characters that have their own books that are also supposed to be part of a team.
I think yuo'd be surprised how little traction Hank Pym has these days. Series like the Ulimates line show that fans are okay with rewriting history. It's no less sever than, say, making Hawkeye a SHIELD assassin. If it makes sense, it works.
It's accurate as it can be given the loose notions about science in comics. Don't know where you got your intel about pym particles, but they are certainly derived from a chemical formula--little gas capsules that originally he'd inhale, and then later just spray on. As for the helmet, that was an application of his skills as a chemist and entomologist, sometimes described as transmitting his vocie commands into pheromones, and at other times translating his language into the ant argot (psuedo-sceince is kind of hard to classify under a particular field). I believe the interpretation of it as some cybernetic telepathy is the latter-day work of Elliot Brown, who often fell back on explaining most super-powers as either psionics (even when the powers ostensibly were not mental in nature) and the shunting of mass from an extradimensional source.
A few years ago, I would have agreed with you. Now, however, there were only 3 non-3D showings on opening weekend at my local theatre, and they were either too early (my wife works until 6:30) or too late (start times after 10pm don't work when you've got two kids who are ridiculous early birds that never stay in bed past 6am).
