kiwi,regarding safety you may have a look at this site :
http://www.airdisaster.com/statistics/
The 737 is one of the safest planes on the market,having also the most number of flights from going into service.
It did evolved over the years,and you can look to a 737-200 ,300 or NG to see that.The 200 is still flying ,by the way.
The NG compared to clasic differes not only by systems,but also by aerodinamics,design.From your question I doubt you even know about the NG 737's.(the -800 ,or even -900XR)
Why not stop also the 747,being an old plane like the 737,right?
What do you mean by 'design' ?
As jetstream rider told you,the 737 was certified for all the modern day requirements.It has all you get on any other plane. EGPWS,RNP-5,RVSM,CAT III ,etc.....
Yes ,it hasn't got a joystick....this is what you mean by design?
Finally,the 737 is not an 'old bus' .Maybe a old bird,or an old airplane but not a bus. The A300 is an old bus....
