I thought about doing an AMA but I don't know that I have anything to say that is interesting enough! :D
The average tenure of the sales field where I worked is around a year to 18 months. The company I worked with subsidizes their sales field pretty heavily though so that's above the industry standard by some margin. The company didn't require inventory to be carried (everything was drop shipped), didn't charge for order processing or a website, and the monthly minimums were fairly low so it made it easy for people to stay in, plus the whole thing is heavily subsidized by the parent company.
The fancy holidays don't just include the seminars, though that's a part of it. There are some reward trips that literally are just that -- fully paid all-inclusives. When I left Big Company they had upwards of 100 sellers who had earned at least one ticket and some who had earned two to the latest one, and this was a slow year.
The seminars themselves could be earned, but this was on a sliding scale (unlike the fancy trips, which once you earned it that was the whole thing including airfare). For the seminars you earned in tiers, the first one being your attendance, the second being the hotel (& food & drink) and the the third being a travel budget for airfare. I'd say most, if not all, of the few hundred attendees earned their attendance, and about 1/3 of that earned their hotel comp. The companies WANT you at the big "rah rah" fest so it was easy, with a ton of ways to earn the levels.
I am out of the business now, but it was fascinating to look at it all from the inside!