On my last trip to Zurich (from LHR), I was most surprised to have to walk through the departures lounge to exit. It just doesn't seem right to be able to mingle with departing passengers!
It wasn't the "departures lounge", just the airside area, since it contained arriving passengers!
Only certain countries have a problem with this.
In the entirety of the USA departing and (domestic/precleared) arriving passengers mix, but obviously international arriving passengers need to go through customs first and have a security check. However, once you have been through TSA you can stay airside indefinitely as long as the airport doesn't close, or you have a flight... I know a few people who have not left the airside area for a week, flying back and forth several times to collect thousands of airline miles on cheap fares (there are overnight flights from west coast to east coast).
This is why TSA at tiny rural American airports can be so anal, because they are scared that they are going to allow a terrorist to get to JFK without any further screening.
The same is true for most of Europe, which trusts EU and USA airports, so it gets quite complicated. From LHR-ZRH, no further security is needed but you do need to enter the Schengen area, but if you are coming from Germany, no security or passport control is needed. If you are coming from Asia, then security is needed if you are transferring, but not if you are exiting into Zurich. However, passport control is needed if you are exiting or transferring to a Schengen flight, but not if you are transferring to the UK.
The UK, however, only trusts security at other UK airports. You can experience departing and arriving passengers mingling when you come off domestic flights to e.g. EDI or GLA. This was also the case at LHR T1's domestic area until the 1990s.