Why do you say that VBox runs best on Windows. I primarily run it on my Ubuntu 8.04 and Ubuntu 10.04 systems {at work and at home} and I support many OSes including {Debian 5, Debian 6, Windows 2000, Windows XP, Windows 7, Ubuntu 8.04 guest, Ubuntu 10.04 guest}. I use the VMs to create disk images I use to install Linux using cloning tools.
I haven't had any problems running vbox on win7 64bit even though i hate windoze.
vbox guys have to only worry about two things developing for windows: 32bit or 64bit.
With linux.......first, which kernel?
Then, are there any conflicts with the many different libraries.
They have just a few pre-built binaries for different linuxes.
For the rest of the distros, you'll have to roll the dice with the generic one. Or you can roll your own from source.
I've had problems where there was no way to install linux with kernel 2.6.x on virtualbox 4 on i3/i5/i7 machines. The CD would simply kernel panic after boot. If I install it on a different machine and transport it to the i3/i5/i7 machine, it will kernel panic. I finally got it to boot by downloading kernel 3+ and compile it a million times with different configs.
Will you tell a beginner to download the vbox source and compile it then roll your own kernel many times and hope that it will work?