I installed VMWare Workstation 7.1.x and Virtualbox 4.0.8 on two different hosts, so I could compare.
I set the virtual network adapter on both to NAT, which was successful for both. The result:
Virtualbox address: 10.10.2.13 VMWare address: 192.168.0.20
The IP assigned to the VMWare guest was expected. But I was surprised by the IP address given to the virtualbox. These machines are on my home network, which only have NAT addresses (192.168.x.x), so when I saw the 10.10.2.x - I was somewhat amazed.
Then I switched both VMs to use bridged networking. The VMWare guest continued to use a NAT address, but the Virtualbox started using a NAT address as well.
In short, I suppose the VMWare guest behavior is what I expected. The Virtualbox behavior was strange to me. If anything, I would have expected the Virtualbox to have done the opposite (use a NAT address for a NAT lan adapter, and a non-NAT address for bridged routine). Don't get me wrong, I was surprised to see the non-NAT address with Virtuabox - under any configuration.
But can someone explain to me why I got the results that I did? And how/why was the IP address 10.10.2.x "working" on my home network?
Keep in mind that both VM guests had successful networking at all times.