Some times it is hard to work part time. I don't know these guys exact situation but I know that for malpractice insurance, you don't get a huge discount for being part time. And if you have overhead (i.e. you run your own office), you have a fixed overhead that you need to meet. And you need to have the same number of CME hours no matter what.
Where I used to work, a bunch of use would have taken the work part time approach. But it doesn't work as well for the company having 2x as many people working half (heck most people would have been ok with just 4 day work weeks) as much even if they didn't pay benefits. Coordinating a large group is most harder than small ones. It really depends a lot on your field as to how well part time works out
These are good points. Although I've read some studies (OK summaries of the real studies) that suggest most office workers who "work" 8 hour days are only doing work for about 4-6 hours. One said as little as 2 hours! Kellogg (the cereal guy) at one point switched his factories to a 30 hour work week and they still produced 35 hours worth of work when compared to the original 40 hour work week. I doubt most of our brains are able to do 8 hours of intellectually demanding work in one chunk.
Companies would not want to have to provide benefits for 2 people instead of 1. But I think we really want everyone to have these benefits anyway, not just the people who can get a full time job. Sorry, I'm drifting off topic. You are right that it can be hard to find a good part time job. The working world isn't very conducive to it right now. If enough of us want it, we can make it better.
As an illustration,
I'm currently 31, using this estimator -
http://www.socialsecurity.gov/estimator/If I keep at my current salary and work until 62, benefits will be $1,915 a month.
If I keep at my current salary and work until 35, benefits will be $870 a month.
If I keep at my current salary and work until 40, benefits will be $1,184 a month.
If I keep at my current salary and work until 67(full retirement), I get $2,771 a month.
It doesn't give me a calculation for retiring early and not taking benefits until 67 though.
I had a pretty significant raise about 4 years ago, so that is probably factoring into it. And this doesn't account for any part time income I would be making during FIRE. If I remember back to the olden days I believe my first job was at 15, not sure that I earned enough for that year to count though. I'd have to work to 50+ to even have a full 35 years of earnings, hoping to avoid that and give up some of my SS benefits.