Every space station built to date has maintained a capsule docked at all times in case the crew had to evacuate. There are so many things that can go wrong in space, as Mir experienced a few years ago. In a short span of time, they experienced a collision with a resupply vehicle resulting in partial depressurization and in another incident, they had a serious fire. There's also the possibility that someone could get sick. A serious illness like appendix attack could be fatal if not treated quickly. Add in other dangers like a collision with space junk and the need for an escape mechanism is all the greater. It just takes too long to wait for the next Shuttle mission (or even a Soyuz) if an emergency occurs. Space is still a dangerous place. Cutting corners will get people killed, as witnessed by what happened with Apollo 1, Soyuz 1, Salyut 1, and the Challenger.

Airliners don't have escape systems because they've been developed over decades to be extremely reliable. With the exception of the deliberate crashing of the four airliners on 911, there has only been one fatal airline accident in the US this year out of nearly a million flights. Malfunctions happen on airliners all of the time. In almost every case, the malfunction isn't severe enough to warrant an immediate landing. In the more severe cases, the airliner has ample opportunity to land within a couple hours.

Likewise, submarines operate in a dangerous environment. Even after 100 years of submarine operations, it's still dangerous as the Kurst demonstrated. Most of the time, a submarine can surface quickly in the event of an emergency.