You are wrong. I did it using iTunes 10.5.2 (11) and Lion 10.7.2.
Of course, there's no one click make ringtone button.
Here's how I did it.
1. Select a title (.mp3) in your iTunes Library
2. Do File > Get Info on selected title
3. In the dialog choose Options tab
4. Set Start Time and End Time (no more than 35 secs otherwise won't work)
5. Close dialog.
6. Now control click the title (right click) and choose Create AAC Version
7. After the creation is finished, delete the Start & End time changes.
8. Delete the newly create title. (no worries here)
9. Open the Trash, rename the title from ringtone.m4a to ringtone.m4r
10. Drag it out of trash into iTunes
Now you have a ringtone.
Make sure it is selected in iTunes for syncing with your new iPhone.