Considering the basic 737 design is almost 50 years old, not exactly surprising.

It would be interesting to learn how current 737s are different: from the original 100-200s, the “Advanced” 200, to the re-engined (300-500) “Classic” series, to current advanced 700-800 series, to the future MAX.
Not just the obvious engines changes, but changes that reduce maintenance and provide greater reliability.
I do wish there were magazines that got into these kind of details. Most airliner mags seem preoccupied with colour schemes.

http://www.b737.org.uk/

Lots of information there.
As I understand it, a 737 rolling off the production line today only has about 25% (or less) parts common to the 200 series.

The Max will have even less in common.