It seems to me that iOS 7 grabs more memory itself, leaving less memory available for the applications, and the devices with 512 MB memory (or less) don't have enough to load aprs.fi in the browser when a lot of stations are brought to view. iPad Mini and iPad 2 have 512 megabytes, the original iPad 1 has 256 MB, the 3rd- and 4th-generation iPads ("new iPad") have 1 GB (specifications).
Sep 22 19:53:51 Minipad MobileSafari
Sep 22 19:53:53 Minipad MobileSafari
Sep 22 19:53:54 Minipad com.apple.launchd (UIKitApplication:com.apple.mobilesafari[0xe421])
The same probably applies to iPhones, but I didn't upgrade to 7 yet.
There's not much I can do about this, other than make it somehow load less stations and lines on the map initially.