Disclaimer, I have NO inside knowledge, just what I've pieced together from this board and having gone throught the process once. The 4-6 week wait after the interview is part of the system, not ideal but that is the way the People department runs it.
The way I understand it, you interview with 3 different people, plus the LOI (line oriented interview, basically the FEDEX CRM trainer deal). All in one day.
Now, once you are done and go home, the interviewers all get together and you go into one of 3 stacks (I think).
1. did great on all interviews, hire.
2. did pretty good, maybe 1 had some qualms, maybe hire.
3. didn't do that great, do not hire, reapply in a year.
Now, the 2nd group is the one that causes most of the delay. Every package goes to the hiring board which is composed of a chief pilot from each base and some People department people. As long as group 1's background checks were good and nobody from group 3 has Herb on the line saying to hire him (who knows?), they presumably spend the lion's share of the meeting on the group 2 guys. Start going through all the Letters of Recommendation, talking to the Chief Pilots, etc.
So, from this not-in-the-know pilot's perspective, the 4-6 weeks is a long time to wait, but the alternative would be to lump everyone from group 2 into group 3 and call it a day. Not really fair. Why not lump then all into group 1? Probably because we think our culture is important enough to take more time/money to get the new hires right. Not saying it is perfect or that good people don't get missed or that jerks don't get hired, just as good as our guys think they can make it. They did add the LOI in the last 3 years.
My 4-6 week wait was from my interview date of 10Sep01 until I found out I got hired on 20Nov01. So, actually my wait was closer to 10 weeks but at least there was nothing big going on with the airlines or military making me doubt my decision to get out or anything. A little suspenseful, but worth it.
Short version. The company could probably let 80% or more of the guys who interview know if they got hired within a few days or a week, but it would probably entail lowering the odds for everyone by kicking anyone who is in the middle to the do not hire stack. I'm not sure where my application was, but I sure wouldn't take that bet. Hey mister, you can find out now but have a lower chance of getting hired or wait 8 weeks and have a better chance, your choice? Deal or No Deal.