I think if you asked the majority of users what they care most about - a smooth experience without UI lag everywhere, or compatibility with the latest apps and updates that are iOS 8 only, they'd choose the former. Moreso when you consider how few apps the average person installs on their devices.
I'd think they would prefer for their devices to work as intended. EG, upgrading to iOS 8 on other devices seems to break traditional iCloud document syncing forcing an upgrade. People care about features as well, which is indicated by the number of people who upgrade every year. People also care about security, which is often neglected in older iOS releases.