Is everyone seeing this on WP81? If so, my guess is that it's due to most of the apps now being "fast resume" (and maybe a bug in the OS), which means they take up memory even in the background (i.e. suspended). Once memory is full, WP81 starts kicking suspended apps out as new apps are loaded. In that case, the "resuming" screen is really a "restarting app" screen.
Compare the time it takes to start a fresh instance of an app to the "resuming" time. If they're similar, that's probably what's happening. I don't know why these crappy phone OSes don't have a virtual memory system so that they can swap to disk (which is basically an SSD) when necessary. Maybe the crappy ARM CPUs don't have VM support?