Stupid question

[Caveman]

Just wondering. When I display a good pic on my monitor, it looks sharp 
bright and contrasty. Now my monitor is small and has a resolution of 
only 72 dpi, so I can't display at 1:1 pixels but only a small part of a 
lets say 6 MP image from the *istD. Now suppose that I could buy a 
monitor with a bigger screen, and same 72 dpi resolution. With a 40x30 
inch screen, I would be able to display the whole 6 MP image. It would 
look as great as a smaller part of it on the smaller screen, at same dpi.
Now just think about trying to print the same 6 MP image on 40x30 inch 
paper. Methinks it would look soft and muddy. How comes it looks great 
on the low 72 dpi monitor and bad on the 300 dpi printer, at same final 
size ?