The numeric keypad is useful to me too. A bit less than the function keys, perhaps, but when entering a list of numbers it works so much better. What's more: keyboards without numeric keypad also tend not to have the section with ins/del, home/end, pgup/pgdn and arrow keys; instead those keys are often arranged in cumbersome and inconsistent layouts. I use those a lot too.
I don't know in exactly which meaning you use the word "atavism", but I do know that having all these keys available, in a familiar layout, is very very useful to me.
Removing them would break compatibility with an awful lot of things, including Windows itself (which lots of people run using Bootcamp or Parallels). Maybe they're weird, I don't know. Momentum is a powerful force, especially when it comes to software design.
Also for the record, Print Screen takes a screenshot on Windows (and on a lot of Linux systems), which is intuitive and simple. Just because you don't use it doesn't mean it's an abandoned key.