To the OP, not every app has its own port, in fact I'd say most don't. The way apps are accessed is by way of a VirtualHost directive in apache, which is running on your HDA.
If the HDA isn't your DNS server then you can work around this by adding DNS entries to the DNS server that you do use, if possible. I don't know what you have as a router and/or DNS server, but I'm assuming it's something like a Linksys or similar router that's doing DHCP, etc. Some of these will allow you to manually add DNS entries, so for the HDA webapps (Listed on
http://hda/setup?sub=webapps&tab=app), all you have to do is create a DNS entry for each one pointing to the IP of your HDA. The HDA will know which webapp you're wanting by way of the URL in your browser and it'll route you to the proper app.
This is how I have it set up, my HDA doesn't do DHCP or DNS for my network but I can still get to my web apps no problem once I manually add them to DNS.