As I suspected. The problem lay with the NS servers for vasoftware.com.
There was intermittant issues with their name servers yesterday. They host the three above sites on your list above. I did some research and found their website for their DNS admin contacted him and he confirmed my issues
So the reason it could be accessable on one DNS server and not on another, is probably just an issue of DNS caching. One DNS server could have a longer cache time than when the server went down.
You need to know about DNS (or have a good understanding to understand why it happened)