One thing I love about dvorak that that layout doesn't have is ' , . not on the bottem row as they are used so often.
Actually if you look at the frequency of letters and punctuation, there are enough letters to occupy all of the home row and top row (assuming 10 letters on each of those rows) before they become less frequent that punctuation unless you want to put the comma on the top row but not the period because the least common of the letters you put on the top row is arguably close to the comma but far more frequent than the period.
A better place to put the punctuation is the two locations on the bottom row on the same side as the vowels (so left for dvorak, this is because you are more likely to end a word on a consonant so punctuation should be on the side with vowels to favor alternation) that are attributed to your index finger as the index finger has the easiest time of reaching the bottom row (try it and you'll see). So on dvorak, the punctuation should really be comma where V is on Qwerty and period where B is on Qwerty.
This works out better if the vowels were on the right side, as B is kind of far for the left hand whereas using N and M for comma and period respectively is a bit easier. I'm working on a layout that does this.
I don't know why everyone keeps those in place for an otherwise excellent layout. Also, I see no reason why ZXCV should stay. There's too much work going into good layouts that are ultimately hurt by these flaws.
C and V should likely be free to move because they are somewhat common, but when it comes to Z and X, they will definitely find themselves on the bottom row anyways. Since they are so infrequent at around 0.7% and 1.5% usage respectively, you don't stand to gain much. They also happen to be on some of the worse places already anyways, as the pinky and ring finger are the two worst fingers. If you were to place the two least common letters on the bottom row pinkies, they would be Z and Q. If you were to place the next least two common letters on the bottom row ring fingers they would be J and X. This puts them right back where they are already (though maybe you might want them on the right hand side or you might put some sort of symbol in those spots instead)! So because it would make very little difference even if you did move them around, it doesn't hurt to just keep them in convenient (close to Ctrl) and familiar places.
If you place letters on rows strictly in terms of frequency, the letter V ends up on the bottom as well and is the most common of the bottom row letters, so having it where it is on the left index finger is actually pretty good. This is assuming vowels are on the right, which they are in this layout and in Colemak for the most part. Dvorak is the only layout that has all the vowels on the left and if you dig into the statistics you can see that this isn't as good as it could be. You might be able to make V slightly better somewhere else on the bottom row but it wouldn't be all that much and then you sacrifice some convenience in it's usage as paste (if you are a programmer, you might use V for paste more than you do for actually typing!). I could go either way on this, there are good arguments to move it and to keep it.
The letter C though has no business being on the bottom row where it is. Luckily though with ZXV where they are you can still sort of emulate a copy by doing cut then pasting it back right where you cut it. Then you have a copy on the clipboard and you have the text you wanted to copy in it's original place still! This only works for text you can edit though, as you can't cut non-editable text.