And the majority of Android users does not install applications outside from Google Play Store either, and the lastest malwares that appeared for Android are from places outside Google Play Store. So where is the point?
If the user jailbreak (iOS)/allow external applications (Android), they increase the chances of malware simple of the fact that there is nothing Apple/Google can do outside App Store/Google Play Store. If they don't, the chance is reduced by far (however it is not 0, there is cases of malwares in both App Store/Google Play Store; the most recent case was in App Store btw).
