You didn't mention what OS you're using, so I'll just mention how to make ringtones on a Mac and a PC.
For Macs, just open up GarageBand 08, drag a song from the Media Sidebar [under iTunes music] into a new track, and "Share > Export to Ringtone". You'll be prompted to select a ≤40s section for the ringtone loop, just drag the orange bar on the top, and extend if necessary. Add fade effects by adjusting the track volume. Once you're done, Garageband will compress into an m4r file and put it into iTunes under 'Ringtone'. For this method, your file must be playable in iTunes, and not DRMed under FairPlay.
For Windows, There's a CNETTV video on how to do this, but I can't remember the link, so just go to cnettv.com, search for 'iPhone ringtone'. It's shown on a Mac, but as long as you have un-DRMed songs, iTunes, a keyboard and a mouse, you can do it. It involves limiting the start and stop point in the music, converting the songs to AAC, renaming the extension to ".m4r", and importing the newly renamed file into iTunes.
That is incorrect. You can create your own ringtones. Garageband on the Mac will allow you to create ringtones. There is something similar for a PC but I don't know what it is called.
Apparently, you did not read everything included with the entire link provided since your conclusion is incorrect.
The many methods for using custom ringtones link includes purchasing ringtones from the iTunes Store, which is one of the many methods and provided first with the link, but is not the only method available.