Stephen -- Inflatable liferafts are carried by virtually all passenger vessels, but not for paying customers. Except on very small ships the rafts are for the crew. And, there are evacuation slides and other devices approved for certain situations. The reality, however, is that it is impossible to achieve 100% success in evacuating a sinking ship except by pure chance.
Probably the most innovative devices are those employed on oil rigs where the crew may have to escape from dizzying heights.
The question is always cost/benefit ratio. How much are you willing to pay for a very small increase in personal safety? Most people will pay something for their well-being, but everyone has a limit forced either by their budget or their perception of risk.
Perception is not always reality. Primarily because of Titanic, the public has worried about "one seat for everyone aboard" in lifeboats. Regulatory agencies have recognized that is only part of the problem. They have forced improvements in lifeboats ranging from permanent covers to motors in place of "ash breeze" (oars). But until this year there has been no public concern about the other end of lifesaving--getting people back out of the lifeboats. Now, the U.S. Coast Guard and other port state agencies are finally studying the problem of "mass casualties" at sea.
What value is there to getting 100% of a ship's people into lifeboats if you can't get them back out safely? This is the current "big question" because solving this problem will yield more immediate benefit (lives saved) for the cost than minor improvements in lifeboats.
The short version to the Captain Dave's above reply is: "Not excatly." The problem here is that very shape and form of the hull limits where you can put lifeboats, and the boats as well as their davits/slides/hoists or any other gear used for stowage and launching are very space intensive.
As to getting them out once they're in the water, there's a sticky wicket for you. If the seas are dead calm, it's not that big a deal but if they're kicking up, then things get "interesting" in the ancient Chinese curse sense of the word. The Carpathia ran into this problem on the morning of 15 April when bringing Titanic's passengers aboard for just that reason.
Getting out of a boat bobbing and heaving in heavy seas is not the safest thing in the world to do. I Know, I've done it when hopping onto my ship from a boat used to ferry the liberty party to and from the ship. Even for the able bodied, it can be an adventure. For a passenger on a commercial vessel, some of whom are anything but able bodied, adventerous can mean lethal.
Hoisting a boat back into the davits in heavy seas is often just as dangerous. You have to hook the falls up and if you're heaving, pitching, and rolling all over the place, you can lose some fingers or even your limbs this way, or get your skull cracked by the heavy weights and hooks at the end of the falls.
This is why boat operations are not undertaken lightly on any ship. Even naval vessels which practice at this all the time.