Yes, It has usually has to do with you XF86Config file. It's your configuration file for X windows and it is located in the /etc/X11 folder, although it location may vary, There are several things that can limit your resolution, if you didn't change anything in your XF86Config file it is likely that the drivers or video card simply does not support this. The nv drivers are somewhat software driven, meaning that it uses CPU time is used in the rendering instead of using the video card, so I suppose you will get quite a bit more flexability,
If you want to check out your file to make sure that it isn't your config file limiting the display size here are 2 sections you should check out. These exerts are from my config for the computer I am using right now, but it can differ quite a bit depending on your tastes.
Section "Monitor"
Identifier "Monitor0"
VendorName "My custom config"
ModelName "Cheapo LCD"
Option "DPMS"
HorizSync 30-60
VertRefresh 50-75 #(this and above line is basicly your monitors "drivers" if the refresh is not high enough for certian resolutions then you can't run them.)
DisplaySize 304.1 228.1 #(optional)
EndSection
Some distros Like SuSE still use Modelines... It's a obsolete method were you specify each and every specification of monitor for each and every resolution instead of the sync ranges, realy irritating, but specific.
Newer method is what I use and most use:
Section "Screen"
Identifier "Screen0"
Device "Card0"
Monitor "Monitor0"
DefaultDepth 16
SubSection "Display" #(this sets the display resolutions and color depth.
Depth 16 #(only depth I have specified in this config is 16bits pseudo color, others are 8 bits and 24 bits. 24Bits =32 bits because part of the 6 bits is used for extra infomation per pixel that doesn't have to do with color ranges)
Modes "1024x768" "800x600" "640x480" #(this line isn't used all the time, but I use it whenever possible)
EndSubSection
EndSection
Check out the man files for more specifics and different options you can use. type: "man XF86Config" at the command line for the man file.