I'm attempting to keep this as simple as possible for you so you can make the best decision for yourself, however I must say a lot of tech has changed and been added since Vista.
That said > This is my conclusion unless someone knows different. One does not need an MS account (which includes Hotmail, Live, and/or Outlook.com) to use the Windows 8/8.1 Mail app as explained here on the MS Windows site:
Do I need to sign in with a Microsoft account to use Windows Live Mail? - Sign in with a Microsoft account to use Windows Live Mail. Of course, they are promoting there services there, of which one does not need to use. Personally I find them convenient. Because I have a MS account, I can add what they call "alias accounts" (including POP) via Outlook.com so to be able to use in the 8 Mail app.
One can add any IMAP or EAS account such as those listed by opening the Windows Mail app > Charms bar > Settings > Accounts > Add an account. Unfortunately the app does not support POP and, I think, for good reasons. One is that POP deletes mail from the server once it has been retrieved whereas IMAP and EAS keeps a copy on the server for to retrieve again by the same device/PC or another Device/PC. I would imagine some companies like POP for it relieves server space whereas other companies offer the service for customer convenience.
So to advise you with the options you have as I see it.
1) I explained the work around above in post #3 and will explain how to configure that if you'd like. Keep in mind that only receives mail > not send using the 8 Mail app.
2) Get an Outlook.com account to configure and use your Roadrunner account as alias.
3) Download the WLM portion of Windows Live Essentials which supports POP as you've been using.
4) Get Office Outlook which I believe supports POP.
5) Find another 3rd party program that does so.
Here is the link to Windows Live Essentials if you decide to go that route:
Windows Essentials: Other Programs - Microsoft Windows. The install program gives you the choice of what programs you would desire to install as it goes along.
Of course, I don't know it all and there may be other options that someone else may have. Please let us know if you need further help.
Edit:
I forgot to add this page of which may be of interest to you, especially to contact your email provider:
Using email accounts over POP on Windows 8 and Windows RT