Redeeman,
If you can provide some contrasting examples, we can work through some of deltas between distributions.
NVidia have slightly different approaches but typically fall down in similar positions (except the DRI/GL interfaces since they completely replace that - this lowers the switching cost to NVidia and makes it work easier, but considerably increases the switching cost to anything else).
There are a few areas that could be called stress points with the distribution. In general these are the kernel, X ABI and more recent DRI/GL interfaces. Distributions or users going bleeding edge (.99 or .90 X versions), -rcxx kernels, complicate the matter more. Then hardware/kernel interplay is also a big factor.
Realistically, a lot of the posts of problems leave out critical information that would allow users to see trends. AGP vs PCIe vs PCI, AGP Chipset, CPU, Memory, kernel, distribution, etc. All of those have an impact on the system.
A lot of posts just say "my 3450 doesn't work". That could be any 1 of 3 product families (PCI, PCIe, AGP), on any number of distributions. Then config files and other critical information is ignored, or if it is presented, then it contains clearly cut and pasted items from forums across the internet. I am not saying the driver is perfect, but a lot of the time there is precious little information to understand the issues or establish trends. (Trends are needed to determine if it is broken hardware for a single user, to ensure internal repeatability).
Realistically,
NV News Linux Forum shows lots of issues with NV drivers. Graphics drivers are complex beasts (we currently support 301 different pieces of hardware within the drivers), and as John says there are more distributions than developers.
Regards,
Matthew