Yeah, autovacuum was added in 7.4 (2003) and not really to be trusted to do its job without monitoring until 8.3 (2008). But the priorities of the PostgreSQL project have changed in the last about 5 years. Today usability is important.

There's a huge difference. Postgresql was formally correct first, then it became fast, then it became easy to use. I always had the feeling I could trust it with my data. Postgresql, if wrong, would be wrong towards correctedness and towards data safety, at the expense of speed.

I definitely don't get the same vibe from MongoDB.

Back when Postgres didn't have automatic vacuuming, the need for manual vacuuming was one of the commonly-suggested reasons why MySQL was a better option - after all, MySQL just worked out of the box.