It seems like it would be easy enough to build a website for free with minimal overhead and have very targeted advertising to cover costs / make a profit.
Also -- shameless plug -- if you're a RoR hacker: http://gopollgo.com/about/jobs
2. Building communities is hard and expensive (for both prospects as well as attracting listings).
3. The alternatives (recruiters) are really expensive (tens of thousands of dollars for some positions), the relatively small fee of these sites is very reasonable for most companies who are serious about hiring a new candidate.
4. This may sound odd, but companies like to spend money for services. If you have purchasing authority at a company you're more likely to go with a paid alternative even if its only marginally better, bosses are more interested in results than expenses (usually).
BTW, your posting is a little contradictory. In bold you write, "Nonetheless, you should be ready to make working on GoPollGo the primary focus of your life" but then state "We don't care what hours you work."
Because people only look for a new job rarely, it's very hard to build a brand for a job site. Hence job sites have to advertise continuously to sustain traffic levels.
A job site which offered free job adverts couldn't buy traffic and hence would be mostly useless to companies looking to hire.
There are also many successful niche job boards that don't buy traffic. I find that most of them rely heavily on organic SEO along with strategic partnernships and even some brand building.
Yes, arbitrage is big in the job board industry (which is why Indeed does so well), but I think that you're overstating its importance.
Especially if you're talking about professional jobs, generally most talented professional are rarely actively looking for a new job, so it doesn't matter how powerful your brand is, you still need to be actively pushing them to look for a new job.
There are very few niche players who succeed on organic SEO, certainly in the tech sector, most of the successful non-ad-buying job boards are run by sites which already have targeted organic traffic.
Building an online talent community isn't easy. I know since I've been doing it for the past 3.5 years. If you can consistently deliver high quality candidates, then you can demand a really high price. This means that you either need to be really big or really targeted. Targeted is better, but most of the big names in the jobs space go for big.
Bigger cities are even more expensive, ie San Fran, NYC. I'll agree that the job postings on craigslist don't look spectacular, but with a few friends who just found jobs and other who are currently jobless, their go to job site is Craigslist. Sure they fill out profiles on Monster and Career Builder, but then they just sit back and wait to be contacted by recruiters.