Some of the zinc pennies I come across while sorting sure have deteriorated in their short life span. The copper pennies from years past hold up so much better. I took samples from a box of pennies I sorted today to show what I mean.
2004-D
Sure I saw a few 2004-D's in the box that were cleaner and shinier than this one but it is pretty common to see zincs looking like this or far worse.
1974-D
Here's one that goes back another 30 years. Look at that nice copper. The other 1974-D's from the box were more brown than this one but look how well this one has held up all these years.
1944-S
Going back another 30 years and the copper pennies are still pretty solid (ok, this one is extra nice but imagine what the 2004-D will look like in another 60 years. )
Now if only I had found a 1914-D or 1914-S in the box to continue my comparison...