Wrong, wrong, wrong. There are viruses out there now that will guess your IP address and install themselves onto your computer if you don't have the right ports blocked. You don't even have to download anything. It finds you. You <i>need</i> a firewall if you want to avoid viruses.
I have been told that the most commonly used Windows exploits are done via NetBIOS. I wouldn't recommend unblocking it. If you do, you'll probably just get hacked. But at least people will be able to browse all the files on your computer.
Anyway, yes, all ports numbers route traffic to the same programs on all computers. Usually. Here are a few example lists.
http://www.chebucto.ns.ca/~rakerman/port-table.html
http://www.iana.org/assignments/port-numbers