There was a time when Apple really and truly cared about their products and their users experience. Those days are long gone as they have started playing "catch up" to Samsung and other companies. They have been rushing to meet the release cycle instead of taking time to actually test their products. Last year we saw stats show that Android crashed less than iOS 7 and now iOS 8 is crashing even more than its predecessor. Just another reason I'll stay away from the fruit.
Crashes will be a result of both bugs in iOS 8 and buggy apps, and so over time as iOS and app updates are released, this figure should do down. It's possible too that older handsets are running old apps that either haven't been updated, either because the user hasn't applied the update or because the app has been abandoned by the developer and won't see any further updates.