You seem to have gotten mixed up somehow about the relationship between DNS, Reverse DNS, and web server virtual hosts.
First of all, know that Reverse DNS lookups are a specific kind of DNS lookup, and that they have absolutely nothing to do with making web server vhosts work. I'll explain more about what they
are good for at the end.
You can configure your web server with all the vhosts you want. A vhost for
www.yourdomain.com, a vhost for
www.linode.com, a vhost for ha.ha.ha.ha....... but no web browser will ever see those websites unless those names 1) exist in DNS and 2) resolve to your server's IP address.
Right now, let's pretend that I have my web server configured with a vhost for
www.linode.com. What happens you enter
http://www.linode.com/ into your browser? Your browser looks up that name and connects to that server, and guess what... it's not my server. The name does not resolve to my IP address.
Right now, I actually do have a vhost for
http://state.gov.zz/. Try clicking on that link. What happens? Nothing, because your browser cannot resolve that name. As far as your web browser knows, it doesn't exist.
So in order for web browsers to find your web server, the name has to exist in DNS, and it has to resolve to your IP address. Once that's all set, your web server will actually receive connections when people enter the name into their browsers.
Now let's look at the opposite situation. Let's say you've got DNS all set up, and your web server is running, but you don't have a vhost for the name. What happens when a browser requests something from that website? Your web server has to send
something, so what it does is it searches the list of vhosts, finds that none match, and then goes back to the first one on the list and serves the content from that vhost. That's why people like me always create a default vhost and put it first in the configuration, and then create subsequent vhosts for each real domain that the server is supposed to serve.
Basically, in order for a web server virtual host to work, both need to be set up.
Now, Reverse DNS is a different business. It's generally only used for logging or displaying client connections. For example, if you were to run a web browser on your linode and connect to my web server, my web server would have your IP address. However, my web server will try to do a reverse lookup to get the hostname, so that it can write that to the log instead of the IP address. The same sort of thing happens when you connect to IRC. The IRC server does a reverse lookup to get your hostname as uses that in your hostmask instead of the IP address. Having reverse DNS set to your own hostname vs. the default generally doesn't actually make anything work any differently. There are exceptions, but you can safely ignore them.