HTC EVO 4G :: Deleting All Sense UI Home Screen Customizations

I had to delete all of my HTC SenseUI home screen customizations (wallpaper and icons) today. I accidentally caused the problem myself, though I think Sense could have been more clever about stopping me. What happened was that I saw a new notification "Ringtone App downloaded." I had not downloaded it, and my son had just been playing with the phone, so I figured he must have done it. I deleted the application, and the phone warned me that it would "reset my icon on the home screen" or something like that. I blithely said OK and deleted the thing. Then, when I went back to the home screen I got the message "The Application HTC Sense (process com.htc.launcher) has stopped unexpectedly." The only option available was "Force Close," and soon as that was pressed the message would appear again.

I was able to get out of it by following the instructions at this HTC Desire page . Now my phone is fine again, but I need to repopulate my 7 home screens.
Two questions:
(1) Why did the Notifications bar tell me this app had been downloaded? My son later said he had not done so. Could it have been an automatic update by HTC?
(2) Am I now missing some sort of Android or HTC ringtone app? I don't normally use ringtones other than the built-in ones but it would be nice to know whether I deleted a standard-issue app and how to get it back if desired.